Biotin, or vitamin B7, is a water-soluble vitamin involved in cellar energy metabolism. It also regulates immunological and inflammatory functions. Biotin is found in foods such as beef, liver, egg yolks, and salmon. It is endogenously synthesized by the intestinal microbiome.

Acquired biotin deficiency causes periorificial exfoliative dermatitis with a "mask-like" appearance, glossitis, conjunctivitis, and alopecia. In addition, individuals with biotin deficiency can develop neurologic symptoms including altered mental status, hallucinations, depression, lethargy, myalgia, paresthesia, and generalized hypotonia as well as nausea and anorexia.

Risk factors include consuming large amounts of raw egg whites or receiving long-term parenteral nutrition. Avidin is a protein found in egg whites that binds biotin, thereby reducing its absorption. Pregnant and lactating individuals are at increased risk due to increased excretion of the biotin metabolite 3-hydroxyisovaleric acid. The risk is higher in cases of hyperemesis gravidarum. Several medications, particularly antiepileptics (carbamazepine, phenobarbital, valproic acid, and phenytoin), may increase the risk of biotin deficiency. Isotretinoin has been implicated as a cause through decreasing biotinidase activity. Excessive alcohol consumption and tobacco use (especially in women) are other risk factors. Antibiotic consumption may cause gastrointestinal tract microbiome imbalances and increase the risk for biotin deficiency. Similarly, individuals with gastrointestinal disease such as inflammatory bowel disease may suffer from biotin deficiency due to reduced endogenous synthesis. In infants, amino acid formulations and modified milk that does not contain biotin may pose a risk as well. Elderly individuals and malnourished children are also vulnerable to biotin deficiency.

Inherited biotin deficiency, as seen in multiple carboxylase deficiency, is discussed separately here.