Skin, disorders of the

The skin is vulnerable to various disorders, including birthmarks and other naevi; infections that may be viral (such as cold sores and warts), bacterial (for example, cellulitis), or fungal (such as tinea, which causes athlete’s foot); rashes due to vitamin deficiency or the side effects of drugs; and tumours, both noncancerous and cancerous. Acne is common in adolescents and is partly related to the action of androgen hormones. Inflammation of the skin occurs in dermatitis, eczema, and skin allergy. The skin is also vulnerable to injuries such as burns, cuts, and bites (see bites, animal; insect bites).