People who frequently consume raw eggs in mayonnaise, Caesar dressing, or eggnog may want to be cautious. Avidin, a protein found in raw eggs, can bind to biotin and stop it from being absorbed. Eggs that have been cooked are not a problem because avidin is broken down by heat.

It is known to affect the results of tests for certain hormones, including thyroid-stimulating hormone, also it may affect vitamin D, and troponin, a biomarker for heart attacks, tests results.

Since biotin is water-soluble, any additional amount will be expunged through urine. No evidence in humans has shown a toxicity of biotin even with high intakes. Because it is water-soluble, any excess amount will leave through the urine. There is no established upper limit or toxic level for biotin.

There’s no single “best” age for biotin. The recommended daily allowance (RDA) varies by age and situation. It’s generally safe for most adults and children (once they reach the recommended ages).

Biotin deficiency can lead to hair loss, so supplements might help in those cases. However, strong evidence for biotin improving hair in people without a deficiency is limited. It might help prevent hair loss for those with existing deficiencies.

Biotin is generally safe for the kidneys at recommended doses. There’s no reported kidney damage from biotin.

Similar to hair, biotin deficiency can cause skin problems. Supplements might help with skin conditions linked to deficiency. However, research on biotin directly improving skin health in those without deficiency is limited.