Other people lose hair because their immune system starts attacking their hair follicles in what is known as autoimmune alopecia. Autoimmune forms of alopecia can be caused by discoid lupus erythematosus, which can lead to sores and scarring on the face and scalp. Central centrifugal cicatricial alopecia is another immune-related condition that causes scalp scarring and permanent hair loss. C.C.C.A. almost exclusively arises among Black women between ages 30 and 55, and research suggests it may afflict as many as 15 percent of such women.
Another common form of autoimmune alopecia is alopecia areata. When people talk about alopecia, they are often referring to this type, which affects one in every 500 to 1,000 people in the United States. It’s unclear what kind of alopecia Pinkett Smith has, but her appearance suggests it is alopecia areata, said Dr. George Cotsarelis, a dermatologist at the Perelman School of Medicine at the University of Pennsylvania.
When, why and how does alopecia areata occur?
Alopecia areata can arise in childhood, adolescence or adulthood, Dr. Lamb said. People who have the condition tend to lose hair in clumps, she said, causing round bald spots. (The word “areata” refers to the patchy nature of the hair loss; when a person loses all their scalp hair, it’s called alopecia totalis, and when they lose all their body hair, it is referred to as alopecia universalis.) Some people with alopecia areata lose patches of hair only on their scalp, while others lose it elsewhere on their body as well, she said.
More than half of the time, hair that has fallen out grows back within a year, Dr. Cotsarelis said. But often, months or years later, people develop other bald patches, too.
It’s unclear what causes alopecia areata, but Dr. Lamb noted that it can have a genetic component. If a parent has alopecia areata, for instance, their child has a one to 10 percent chance of developing it too, she said. Alopecia areata can also be triggered by stressful events and by nutritional deficiencies, such as iron deficiency, Dr. Cotsarelis said.