Cosmetic labs are testing facilities that use a variety of scientific methods to evaluate the safety and effectiveness of cosmetic products. Types of tests performed by cosmetic labs include chemical analysis, microbiological testing, and skin irritation testing.

Cosmetic lab testing can help ensure that products you use on your skin are safe and effective. Testing can also help identify potential adverse effects of products on your skin. You can even search online for more information about lab testing for cosmetic products.

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For example, if you're using a new sunscreen lotion, it may be important to test it in vitro (in the lab) before using it on your skin to make sure it doesn't cause skin irritation.

Testing can also help identify ingredients that may be harmful if taken in high doses or if applied to large areas of the body. For example, testing has shown that some chemicals used in hair dye can be toxic if ingested or absorbed through the skin. 

For example, it would be very difficult for independent labs to test individual ingredients in skin care products because they are so small, they're often included in tiny amounts and may be masked by other ingredients. 

However, manufacturers can test their products for safety by submitting samples to laboratories that run tests on foods and drugs.

The FDA requires all manufacturers of cosmetics, including skin care products (including toothpastes), hair care products and body care products containing more than 0.1% of any single ingredient used there in the past year to register with the agency through a process known as Cosmetic Registration Branch (CRB).