Skin diseases are extremely common but their exact prevalence is unknown. There are over 1000 different entities described but two-thirds of all cases are due to fewer than 10 conditions. These common conditions include acne, warts, eczema, infections due to bacteria, viruses and fungi, and psoriasis.
Some conditions, e.g. acne, may be part of normal development while others may be inherited, e.g. the Ehlers-Danlos syndrome. Skin disease may present as part of a systemic disease, e.g. the rash associated with systemic lupus erythematosus (5LE), or alternatively a severe skin disease, e.g. pemphigus, may cause systemic symptoms. Geographical factors are also important; in particular, skin conditions due to certain fungi and bacteria are more prevalent in the tropics.