A desert is a region of land that is very dry because it receives low amounts of precipitation (usually in the form of rain but may be snow, mist or fog), often has little coverage by plants, and in which streams dry up unless they are supplied by water from outside the area.
Alopecia areata is an autoimmune disease. Autoimmune means that the body's immune system attacks the body. When alopecia areata develops, the body attacks its own hair follicles. A person's genetic makeup, combined with other factors, triggers this form of hair loss.
Alopecia areata causes a unique form of hair loss different to the more common age-related male and female pattern hair loss. It's also the most common autoimmune disease (when the body's immune system attacks its own tissues), more common than insulin-dependent diabetes, rheumatoid arthritis or thyroiditis (inflammation of the thyroid).