Best Crowdsourcing Websites for Your Next Project in 2024

Photo of author
Written By David Pate
Best Crowdsourcing Websites

In a world driven by connectivity, innovation challenges and collaboration, a revolutionary concept has emerged, transforming the way we approach problem-solving cad design, innovation, and creativity. Welcome to the exciting realm of crowdsourcing, where the collective brilliance of the masses converges to create wonders previously thought impossible, all made possible through the power of crowdsourcing websites.

The crowdsourcing websites evolved as its niche changed. a few focus on innovative ideas. Some focus on technology, while others are general-purpose markets that do virtually all kinds of work for online communities.

Page Contents show

Evolution and Growth of Crowdsourcing Platform

The concept of crowdsourcing isn’t entirely new; it has evolved over time with the advent of digital technologies and the internet. From humble beginnings as a niche practice to a thriving global phenomenon, crowdsourcing platforms have proliferated, providing accessible avenues for collaborative endeavors.

The Impact of Crowdsourcing on Innovation and Problem Solving

The impact of crowdsourcing on various industries and domains cannot be overstated. It has become a driving force behind groundbreaking innovations, enabling businesses and organizations to access an unparalleled pool of talent and fresh perspectives. By crowdsourcing ideas and solutions, problems that once seemed insurmountable now find ingenious resolutions.

Crowdsourcing has also revolutionized the traditional approach to problem-solving. Instead of relying solely on internal expertise, companies can now leverage the collective knowledge of a diverse crowd, ensuring comprehensive and multifaceted solutions.

Best crowdsourcing platforms

What are Crowdsourcing Platforms?

Crowdsourcing platforms are dynamic online hubs that epitomize the synergy of human creativity and technological innovation. These virtual arenas serve as melting pots of diverse talents, bringing together individuals from all walks of life to collaborate and tackle a myriad of challenges. From small-scale tasks to ambitious projects, crowdsourcing platforms harness the collective intelligence of the crowd to yield ingenious solutions.

In a world driven by interconnectedness and boundless collaboration, these platforms have emerged as game-changers, redefining how organizations approach problem-solving and tapping into an unparalleled pool of human ingenuity.

Best crowdsourcing platforms

Advantages of Crowdsourcing Websites:

1. Diverse Perspectives and Ideas

One of the most significant advantages of crowdsourcing websites is the vast pool of diverse perspectives and ideas they offer. By involving individuals from various backgrounds, cultures, and areas of expertise, these platforms bring forth a wealth of fresh and innovative solutions to complex challenges.

2. Cost-Effectiveness

Crowdsourcing provides a cost-effective alternative to traditional methods of project execution. Instead of hiring specialized teams or experts, businesses can tap into crowdsourcing platforms to access a wide range of talents at competitive prices. This significantly reduces operational costs and enables organizations to allocate resources more efficiently.

3. Global Reach and Accessibility

Crowdsourcing websites break down geographical barriers, allowing businesses and public sector organizations to reach a global audience of contributors. This global reach opens up new markets and facilitates access to talent and ideas from around the world, expanding the possibilities for growth and collaboration.

4. Faster Turnaround Times

The collective nature of crowdsourcing enables quick and efficient problem-solving. With a diverse group of contributors working simultaneously, projects can progress at a faster pace, leading to quicker turnaround times and timely delivery of results.

5. Flexibility and Scalability

Crowdsourcing platforms offer unmatched flexibility and scalability. Whether it’s a small task or a large-scale project, businesses can adapt their crowdsourcing efforts to suit their specific needs. This agility allows organizations to tackle a wide range of projects, regardless of their scope or complexity.

6. Access to Specialized Skills

Crowdsourcing websites host a plethora of specialized skills and expertise that might be challenging to find within a single team or organization. Businesses can access talents ranging from graphic design and software testing to marketing and product development, enabling them to execute complex projects that require diverse skill sets.

7. Customer Engagement and Feedback

Crowdsourcing can be an effective way to engage customers and involve them in the decision-making process. By using new innovation challenges seeking customer feedback and ideas through crowdsourcing initiatives, businesses can strengthen their relationship with their audience and gain valuable insights for improving products and services.

8. Risk Mitigation and Testing

Before fully committing to a project, businesses can use the right crowdsourcing platform to test ideas, concepts, and prototypes. This approach helps in mitigating risks and ensures that resources are directed toward viable and well-received solutions.

9. Increased Innovation and Creativity

The collaborative nature of crowdsourcing sparks a culture of innovation and creativity. By encouraging contributors to think outside the box and explore unconventional solutions, crowdsourcing websites become hotbeds for groundbreaking new ideas and novel approaches.

10. Access to New Markets and Audiences

For startups and small businesses, crowdsourcing offers an opportunity to access new markets and target audiences. By leveraging the expertise of contributors with an understanding of local markets, businesses can tailor their products and marketing strategies to cater to specific regions.

11. Improved Decision Making

Crowdsourcing platforms enable businesses to gather data, insights, and opinions from a large group of people. This wealth of information empowers organizations to make well-informed decisions based on the collective wisdom of the crowd.

Best crowdsourcing platforms

The Different Types of Crowdsourcing Websites

Diversity is the heart and soul of crowdsourcing, and this is evident in the variety of platforms available. Each type caters to specific needs, ensuring that no creative pursuit is left unaddressed:

Creativity at its Finest: Design Crowdsourcing Platforms

These platforms connect businesses and individuals seeking innovative graphic designs with a global community of talented designers. From logos to packaging, the creative prowess of these artists professional designers knows no bounds.

Tech-Savvy and Solution-Driven: Software Testing Crowdsourcing

Software development and testing are taken to new heights by these platforms, where an army of testers diligently assesses and refines digital products for a seamless user experience.

Idea Generation and Problem-Solving: Open Innovation Platforms

Here, organizations and individuals can pose challenges and conundrums to the crowd, inspiring a surge of creative ideas and out-of-the-box solutions.

Micro Tasks and HITs: Crowdsourcing for Quick Wins

Micro task platforms offer small, straightforward tasks that can be completed quickly, making them ideal for crowd participation on a smaller scale.

Notable Crowdsourcing Companies and Market Leaders

Within the bustling landscape of the crowdsourcing marketplace, certain companies and platforms have risen to prominence, setting the bar for excellence and innovation:

Amazon Mechanical Turk: The Pioneer of Crowdsourcing

Launched by Amazon, Mechanical Turk (MTurk) pioneered the concept of crowdsourcing and remains a prominent player in the industry, offering a vast array of micro tasks to a diverse global workforce.

99designs: Where Creativity Flourishes

As a market leading organization and design crowdsourcing platform, 99designs brings businesses and designers together to create visually stunning and captivating graphics.

Topcoder: Empowering Technological Brilliance

Topcoder specializes in software development and data science, hosting competitions that push the boundaries of technical expertise and innovation.

Kickstarter: Crowdfunding Creative Visions

Although primarily a crowdfunding platform, Kickstarter has facilitated the realization of countless creative projects through the power of collective funding.

Best Crowdsourcing Sites to Fuel Your Business in 2024

Are you a small business owner or an ambitious entrepreneur seeking innovative solutions without breaking the bank? Look no further! The world of crowdsourcing is a treasure trove of creative opportunities, and we’ve handpicked 15 remarkable platforms that will revolutionize your business journey. From captivating images to jaw-dropping product designs, these best crowdsourcing platforms and websites are your gateway to success. Let’s dive into this exciting realm and uncover the potential of each platform!

1. RedesignMe:

RedesignMe is a game-changing crowdsourcing logo design platform that focuses on revamping and reimagining products and services for the modern world. Whether you have an existing product that needs a fresh perspective or you’re brainstorming ideas for a new one, RedesignMe is the ideal destination to fuel creativity, design thinking and innovation.

How it Works:

  1. Expert Views: At the heart of RedesignMe lies a community of creative thinkers and experts who provide invaluable input on your projects. They offer fresh ideas, constructive feedback, and insightful suggestions to help you elevate your product’s potential.

  2. Design Critique: Share your product with the RedesignMe community and receive candid feedback on what works and what needs improvement. This open and supportive environment encourages diverse perspectives and fosters collaboration.

  3. Redesign Challenges: If a specific concept stands out during the design critique phase, you can actively launch a redesign challenge. Invite participants to submit their innovative interpretations and witness the brilliance of collective problem-solving.

  4. Consumer-Centric Approach: RedesignMe’s focus is on creating products and services that cater to the needs and preferences of modern consumers. Emphasizing user experience and usability, the platform ensures that your offerings resonate with your target audience.

2. uTest:

Usability testing is crucial for businesses aiming to deliver exceptional user experiences across websites, mobile apps, and services. uTest emerges as a beacon of excellence in online testing in this domain, connecting businesses with a vast community of Quality Assurance (QA) professionals from around the globe.

How it Works:

  1. Global Community of QA Professionals: uTest boasts a diverse and highly skilled community of QA professionals hailing from more than 150 countries. Their collective expertise spans various industries, ensuring that you receive comprehensive and meticulous testing.

  2. User-Focused Testing: Whether you’re launching a website, app, or software, uTest ensures that the end-users’ perspectives are at the forefront. Through user-focused testing, businesses can identify potential pain points and address them proactively, leading to an enhanced user experience.

  3. Quality Assurance Solutions: From website design assessments to mobile app functionality checks, uTest offers a range of quality assurance solutions tailored to your specific needs. The platform is versatile, accommodating projects of all sizes and complexities.

  4. Usability Feedback Reports: Following the testing process, businesses receive comprehensive feedback reports highlighting the strengths and areas for improvement. Armed with this valuable data, you can optimize your product or service for optimal performance.

3. Designhill:

For small businesses and startups seeking affordable and professional graphic and web design and solutions, Designhill is a standout option. As a credible marketplace for crowdsourced designs, Designhill connects businesses with a pool of talented and skilled graphic designers, from diverse backgrounds.

How it Works:

  1. Access to a Vast Design Pool: Designhill boasts a large and diverse community of designers, encompassing both seasoned professionals and emerging talents. This wide array of choices ensures that businesses can find the perfect match for their creative needs.

  2. Customized Design Solutions: Whether you require a captivating logo, striking business cards, or an engaging website design, Designhill offers a range of design categories to choose from. The platform tailors solutions to match your brand identity and vision.

  3. Contests and DIY Tools: Businesses can either launch a design contest, inviting designers to submit their concepts, or utilize Designhill DIY tools for a hands-on approach. The user-friendly logo maker, for instance, empowers businesses to create logos effortlessly.

Best crowdsourcing platforms

4. Flickr:

In a world of digital video cameras where visual storytelling reigns supreme, Flickr stands as a creative oasis, offering access to millions of high-quality images sourced from photographers and enthusiasts worldwide.

How it Works:

  1. Vast Collection of Visuals: Flickr’s image library encompasses a vast collection of photographs, spanning diverse categories such as landscapes, historical figures, iconic symbols, celebrities, and more. Whatever your visual needs, Flickr is sure to have an image that captures the essence of your brand.

  2. Catering to Different Budgets: Say goodbye to pricey stock photos! Flickr offers a range of licensing options, including the Creative Commons license, which allows businesses to use images at little to no cost (depending on the license type).

  3. Curation and Copyright Considerations: While Flickr provides a treasure trove of visuals, businesses should be mindful of image licensing and copyright requirements. Always check the licensing terms to ensure proper usage and avoid any legal issues.

  4. Inspiration and Engagement: Beyond being a repository of images, Flickr serves as a vibrant community for photographers and visual artists. By engaging with the community and discovering fresh perspectives, businesses can find inspiration to elevate their visual storytelling.

5. Chaordix:

Chaordix stands at the forefront of the best crowdsourcing platforms around, bringing together the brilliance of collective intelligence and the spirit of innovation. It is a marketplace that thrives on engaging professionals and amateurs alike, inviting their opinions and ideas to solve real-world problems.

How it Works:

  1. Embracing Diversity: At Chaordix, diversity is celebrated. Businesses seeking fresh perspectives and creative solutions can tap into a diverse pool of contributors with varied backgrounds and expertise. This diversity fuels the generation of unique and innovative ideas.

  2. Building Brands with Community Input: For those contemplating brand identity development, Chaordix offers a treasure trove of experts. Businesses can invite experts to provide insights and advice on crafting a powerful brand that resonates with the target audience.

  3. Crowdsourced Solutions: Chaordix is a one-stop solution for businesses seeking ideas from contributors. Whether you need a game-changing product concept or a groundbreaking marketing strategy, this platform has the collective brainpower to transform your vision into reality.

  4. Empowering Decision-Making: Through expert advice and community-driven feedback, businesses can make informed decisions with a profound understanding of customer preferences and market trends. This data-driven decision-making ensures relevance and success.

6. Namethis:

Finding the right name for your small business or startup can be a daunting task. Enter Namethis, a crowdsourcing site dedicated to unearthing the perfect name that resonates with your brand and captures the essence of your offerings.

How it Works:

  1. Name Generation Contest: Namethis operates on the premise of launching a 48-hour naming contest. During this period, a vibrant community of participants suggests creative and catchy names aligned with your brand’s identity.

  2. Inclusive Voting Process: The power of choice lies not just with you but with the crowd. Once the names are in, the community votes on their favorites, providing valuable insights into which names strike a chord with potential customers.

  3. Nominal Fee for Premium Results: To ensure a dedicated effort from participants, Namethis offers a nominal fee to the best three-name ideas. This incentivizes contributors to bring their A-game, guaranteeing you a selection of top-tier names.

  4. Name Validation and Ownership: Before making your final decision, Namethis ensures that the chosen names are available for trademark registration and domain ownership. This protects your brand’s future and potential legal complications.

7. Ponoko:

Ponoko is a haven for product designers and entrepreneurs seeking inspiration and manufacturing solutions solving complex problems. Whether you have a captivating design idea or need expert advice, Ponoko’s designer community is ever-ready to transform your dreams into tangible realities.

How it Works:

  1. Submit Your Design: Share your design concept, be it for a CD cover or any other product, with Ponoko’s vibrant community. This opens the door to a world of innovative suggestions and creative inputs.

  2. Expert Feedback and Cost Estimates: Get valuable feedback from Ponoko’s designers, who can shed light on your design’s feasibility and offer insights on improvements. Additionally, receive cost estimates to determine the financial aspect of your project.

  3. Collaborative Designing: With Ponoko’s collaborative environment, you can engage in interactive discussions with designers, fine-tuning your product concept to perfection. This iterative process ensures that every element is meticulously refined.

  4. Affordable Manufacturing: One of the most remarkable features of Ponoko is its cost-effective manufacturing solutions. You don’t need to break the bank to bring your product design to life, as Ponoko offers budget-friendly production options.

8. Indiegogo:

Indiegogo is the epitome of crowdfunding success, empowering entrepreneurs, artists, and visionaries to bring their ideas to life with the support of a global community.

How it Works:

Launch Your Campaign: Indiegogo allows you to create a captivating crowdfunding campaign to showcase your idea or project. Tell your story through videos and images, inspiring potential backers to rally behind your cause.

Global Reach: With a staggering number of monthly visitors from around the world, Indiegogo ensures that your campaign reaches a vast and diverse audience. Connect with backers who resonate with your vision and become advocates for your success.

Flexible Funding Options: Indiegogo offers flexible funding options, giving you the freedom to keep the funds raised even if you don’t reach your initial goal. This means that every contribution counts and can fuel the progress of your project.

perform online testing


GoFundMe, the heartwarming crowdsourcing and crowdfunding site that, has become a beacon of hope for individuals, communities, and nonprofits seeking support for their dreams and causes. Whether it’s funding a life-changing project, supporting a charitable endeavor, or overcoming personal challenges, GoFundMe is the platform that brings compassion and generosity together.

How it Works:

Personal Stories: GoFundMe thrives on the power of storytelling. Users can create compelling campaigns that share their journeys, aspirations, and struggles. Heartfelt videos, heartfelt images, and authentic narratives resonate with potential donors, inspiring them to make a difference.

Social Outreach: To maximize campaign reach, GoFundMe seamlessly integrates with all social media sites and platforms. Share your campaign across Facebook, Twitter, Instagram, and beyond, and watch your message ripple through the hearts of your friends, family, and even strangers.

Platform Fees: Unlike some crowdfunding sites, GoFundMe doesn’t charge a platform fee. This means more of the funds raised go directly to the cause, making it an attractive choice for those seeking to raise money for personal endeavors or charitable causes.

10. Mightycause:

Mightycause is a dynamic crowdfunding platform that champions the spirit of giving back. Focused on nonprofit organizations and social causes, Mightycause harnesses the collective power of donors to create a lasting impact on communities and society.

How it Works:

Nonprofit Campaigns: Mightycause is home to thousands of nonprofit campaigns, each driven by a mission to bring positive change. Nonprofits can craft inspiring stories, showcase their projects, and connect with donors who share their passion for making the world a better place.

Peer-to-Peer Fundraising: Mightycause goes beyond standard crowdfunding by enabling peer-to-peer fundraising. Supporters become advocates for the cause, leveraging their networks to attract contributions from friends, family, and colleagues.

Giving Days: Mightycause hosts exciting giving days that unite donors and nonprofits under a common cause. These events generate a surge of giving, amplifying the impact of individual contributions and creating a sense of camaraderie among supporters.

11. StartEngine:

StartEngine is a trailblazing crowdsourcing platform that has revolutionized the way startups secure funding. Through equity crowdfunding, StartEngine connects entrepreneurs with a vast network of investors, fueling the growth and success of promising ventures.

How it Works:

Equity Crowdfunding: StartEngine embraces equity crowdfunding, enabling startups to offer equity or ownership stakes to investors in exchange for financial support. This democratizes investment opportunities, allowing everyday individuals to become stakeholders in innovative companies.

Investor Outreach: Entrepreneurs can create engaging campaigns that highlight their business plans, achievements, and potential for growth. StartEngine attracts a diverse investor base, providing startups with a unique chance to access capital from a wide range of backers.

Regulation Crowdfunding: StartEngine operates within the regulatory framework of the JOBS Act, making it compliant with SEC regulations. This ensures a secure and transparent environment for both entrepreneurs and investors.

computer aided design

12. Crowd Supply:

Crowd Supply sets itself apart as a dedicated crowdfunding platform for hardware projects. Emphasizing quality, sustainability, and innovation, Crowd Supply provides a launchpad for inventors and makers to turn their hardware dreams into reality.

How it Works:

Hardware Focus: Crowd Supply exclusively caters to hardware projects, making it a go-to platform for creative innovators in the tech and engineering domains. From cutting-edge gadgets access tools to eco-friendly devices, Crowd Supply showcases the best in hardware ingenuity.

Collaborative Pre-orders: Backers on Crowd Supply place pre-orders for products they believe in, supporting inventors to take their designs from prototype to production. This collaborative approach fosters a sense of partnership and shared success.

Transparent Project Milestones: Entrepreneurs and makers provide backers with detailed updates on project milestones, production schedules, and any challenges encountered. Transparency and clear communication build trust and confidence in the campaign.

13. Fundable:

Fundable serves as a bridge between aspiring entrepreneurs and potential investors, providing a diverse range of businesses with the funding needed to turn dreams into viable ventures.

How it Works:

B2B and B2C Funding: Fundable caters to both B2B and B2C businesses, providing a versatile platform for diverse industries and ventures.

Business Crowdfunding Campaigns: Entrepreneurs launch crowdfunding campaigns showcasing their business concepts, products, or services. Through compelling narratives and enticing rewards, they attract support from backers and investors.

Beyond Crowdfunding: Fundable extends beyond crowdfunding, offering additional services like startup accelerators and opportunities to connect with accredited investors.

14. Wefunder:

Wefunder is more than just a crowdfunding platform; it’s a vibrant community where innovation and investment converge to shape the future. With a mission to support small businesses and startups, Wefunder empowers everyday individuals to become angel investors and back the next big business idea together.

How it Works:

Equity Crowdfunding for All: Wefunder believes that anyone should have the opportunity to invest in promising startups. Through equity crowdfunding, investors of all backgrounds can pool their resources and support ventures they believe in.

Diverse Investment Options: Whether it’s technology, healthcare, or consumer goods, Wefunder offers a diverse array of investment opportunities. Entrepreneurs can launch campaigns that resonate with potential backers, showcasing their vision and potential for success.

Early-Stage Investing: Wefunder focuses on early-stage startups, meaning investors have the chance to get in on the ground floor of innovative ventures with high growth potential.


16. Crowdcube:

Crowdcube is a trailblazer in equity crowdfunding, connecting entrepreneurs and investors in a groundbreaking way. With a focus on transparency and collaboration, Crowdcube has revolutionized the world of early-stage investing.

How it Works:

Open to All Investors: Crowdcube believes in the power of the crowd. It opens up investment opportunities to everyday investors, giving them a chance to back startups, scaleups, and even more established businesses.

A Diverse Portfolio: Crowdcube boasts a diverse range of investment opportunities across industries and sectors. Investors can browse campaigns from technology, retail, fintech, and many other exciting ventures.

Supporting Growth: Startups and businesses seeking funding can launch campaigns on Crowdcube to attract investors and fuel their growth. The platform provides a compelling showcase for entrepreneurs to present their vision.

distributed workforce

FAQs: About Best crowdsourcing platforms

Q: Can I earn from Crowdsource?

A: Yes, you can earn from other crowdsourcing sites! Many crowdsourcing platforms offer opportunities for individuals to contribute their skills and expertise to various projects and tasks. By participating in these projects, you can earn money based on the scope and complexity of the work you complete.

Q: Can you make money from crowdsourcing?

A: Absolutely! Crowdsourcing provides a way for individuals to monetize their skills and talents by contributing to different projects. Whether it’s graphic design, writing, software testing, or idea generation, there are plenty of opportunities to make money through crowdsourcing on such platforms.

Q: What is an example of a crowdsourcing?

A: A popular example of a crowdsourcing project is Wikipedia, where volunteers from around the world collaboratively contribute and edit articles on a wide range of topics. The collective efforts of these volunteers result in a comprehensive and constantly evolving knowledge base.

Q: What do you mean by crowdsourcing?

A: Crowdsourcing refers to the practice of obtaining ideas, services, or content from a large group of people, often through online platforms. It harnesses the collective intelligence, skills, and creativity of the crowd to achieve a specific goal or solve a problem.

Q: What is the crowdsourcing strategy?

A: The crowdsourcing strategy involves leveraging the expertise and creativity of a diverse group of people to tackle challenges, generate innovative ideas, or complete tasks more efficiently. It often involves outsourcing tasks or breaking down complex problems into smaller, manageable tasks distributed among the crowd.

Q: How do I start a crowdsourcing website?

A: Starting a crowdsourcing website requires careful planning and execution. Here are some steps to consider:
1. Define your niche and target audience.
2. Choose the type of crowdsourcing model (e.g., open innovation, crowdfunding, microtasking).
3. Develop the platform and user interface.
4. Attract and engage a community of users.
5. Implement measures to ensure quality and security.
6. Market the platform to both contributors and seekers of crowdsourced solutions.

Q: Is Google an example of crowdsourcing?

A: Yes, Google utilizes crowdsourcing in various ways. For example, Google Maps allows users to contribute and edit map data, improving the accuracy and completeness of the information. Additionally, Google’s “Google Opinion Rewards” app rewards users for completing surveys that help gather data and insights.

Q: What does crowd source do?

A: Crowdsourcing harnesses the collective wisdom human intelligence tasks, and efforts of a group of individuals to solve problems, generate ideas, or complete tasks. It taps into the diverse skills, perspectives, and knowledge of the crowd to achieve specific objectives.

Q: What are the 4 elements of crowdsourcing?

A: The four key elements of crowdsourcing are:
1. Crowds: The diverse group of individuals who contribute their skills or ideas.
2. Online Platform: The digital space that facilitates communication and collaboration among the crowd.
Purpose: The specific goal or problem to be solved through crowdsourcing.
Incentives: The motivations or rewards offered to participants for their contributions.

Q: What is an example of a social media marketing crowdsourcing?

A: Social media platforms often leverage crowdsourcing for various initiatives. For example, Twitter may crowdsource ideas or feedback from its users for new features or improvements to the platform. Similarly, Instagram might invite users to participate in hashtag challenges or photo contests.

Q: Which industry is the most popular in crowdsourcing?

A: Crowdsourcing is prevalent across various industries, but it is particularly popular in the tech and creative sectors. Graphic design, software development, content creation, and idea generation are some of the areas where crowdsourcing thrives.

Q: What is an example of a content crowdsourcing platform?

A: Buzzfeed is an example of a content crowdsourcing platform. It encourages its readers to submit listicles, articles, quizzes, and other content ideas, and some of the submissions are featured on the website.


In conclusion, crowdsourcing has revolutionized the way we approach problem-solving, creativity, and funding. With platforms like Wefunder, LendingClub, and Crowdcube, raising capital and investing in startups have become more accessible than ever before. Meanwhile, GoFundMe and Might cause empower individuals and nonprofits to raise funds for meaningful causes.