What to know about alopecia, Jada Pinkett Smith's autoimmune hair loss disorder

• Will Smith slapped Chris Rock at the Oscars after the comedian joked about Jada Pinkett Smith's baldness.
• Pinkett Smith has alopecia, an autoimmune condition that causes hair loss.

At the 2022 Oscars ceremony, Will Smith slapped Chris Rock on stage after he made a joke about Jada Pinkett Smith's baldness.

Pinkett Smith has an autoimmune condition called alopecia, which causes the immune system to attack hair follicles and leads to hair loss.

While on stage, Rock implied Pinkett Smith could be in "G.I. Jane 2" — referring to the 1997 movie "G.I. Jane," where Demi Moore shaves her head bald, as Insider's Cheryl Teh reported.

There is no cure for alopecia, and people with the condition may experience hair loss in large or small patches on their head and face, but it can also affect other parts of the body.

Alopecia is an autoimmune condition

For most people with alopecia, there are no other symptoms aside from their hair falling out in small patches. The patches are usually round, about the size of a quarter.

Some people experience hair loss that comes and goes throughout their life, while others have one episode that never returns, and the hair regrows fully.

There are three main types of alopecia:

• Patchy alopecia areata: This is the most common type of alopecia and involves hair loss in one or more coin-sized patches on the scalp or other body parts.
• Alopecia totalis: This type involves the loss of all or nearly all hair on the scalp.
• Alopecia universalis: A rarer type of alopecia, which leads to nearly all hair loss from the scalp, face, and rest of the body.

The first sign of alopecia is usually the loss of circular patches of hair on the scalp. For men, however, it can be seen in the beard, and both men and women may notice loss of eyebrows or eyelashes.

For some people, the hair loss is preceded by a tingling, burning, or itching sensation.

Hair can regrow on its own, and outcomes are best for people who lost less hair initially, developed alopecia at a later age, have no family history of the condition, and have no changes in the pits and ridges of their nails, according to NIH.

There is no cure for alopecia and the cause is unknown

While there is no cure for alopecia, there are treatments that encourage hair regrowth. The cause of the disease is unknown but scientists believe there is a genetic component, according to the NIH.

It affects men and women equally, most commonly in the teens, twenties, or thirties.

Pinkett Smith is open about her alopecia

Pinkett Smith has opened up about her alopecia before.

In December, Pinkett Smith posted a video of herself on Instagram in which she showed off her shaved head and talked candidly about her hair loss.

Revealing a bald patch on the top of her head, Pinkett Smith said: "Y'all know I've been struggling with alopecia, and just all of a sudden one day, look at this line right here. It just showed up like that. Now this is going to be a little more difficult for me to hide, so I thought I'd just share it so y'all not asking any questions."

Pinkett Smith opened up about her alopecia on an episode of her Facebook series, "Red Table Talk," in 2018.

"It was terrifying when it first started," she said on the episode. "I was in the shower one day and then just handfuls of hair just in my hands."