Most people suffer no side effects when taking up to 10 mg daily of biotin, but some experience an allergic reaction, including hives or an upset stomach, according to Drugs.com. If the reaction includes swelling of the face or oral cavity, hives or difficulty in breathing, emergency medical care is recommended. Individuals who suffer an allergic reaction once should avoid using these supplements in the future.
Biotin deficiencies are rare, according to MayoClinic, and the Food and Drug Administration has not set a recommended daily allowance for this vitamin. In adults, the normal intake of biotin is between 30 and 100 micrograms daily. Supplements are available in both pill and capsule form, but they are not a substitute for proper diet. Foods that provide biotin include cauliflower, carrots, salmon, liver, bananas, yeast, cereals and soy flour. Cooking and preserving these foods reduces the available amount of biotin they provide.
WebMD reports that doctors most often observe biotin deficiencies in pregnant women or individuals who receive their nutrition through tube feeding. No reliable medical tests are available for these deficiencies, but symptoms include thinning of the hair, a red, scaly rash around the nose and mouth, and problems with the nervous system. Some evidence shows that deficiencies may be a result of diabetes.