Dermatology, the study of diseases of the skin—the human body’s largest organ–is both misunderstood and underrated. Even some physicians in other specialties think it’s “easy,” or borders on the trivial, but skin diseases are important because they are common, impose a huge economic and psychological burden on patients, and can be deadly.

In 2013, one American in four sought treatment for at least one skin ailment, and the average person was treated for 1.6 skin diseases. Nearly half of Americans over age 65 have skin disease, with an average of 2.2 each. Treatment of skin disorders accounted for $75 billion in medical, preventative and prescription and non-prescription drug costs.

Skin diseases are often serious, and many can actually be fatal. The threat of malignant melanoma is well-known, but non-melanoma skin cancer also causes or contributes to significant morbidity and mortality. Moreover, common skin diseases such as psoriasis are associated with serious medical conditions including heart disease and diabetes.

In spite of the importance and frequency of skin diseases, there are many myths and misconceptions about them and the dermatologists who diagnose and treat them. Things you should know: