WATCH | Why Chris Rock's 'GI Jane' joke triggered Will Smith

Many Oscar viewers were caught off-guard by Will Smith's reaction to a seemingly innocent joke by Chris Rock about Jada Pinkett-Smith's short hair cut.

The joke saw Smith jump from his seat and slap Rock across the face before shouting that Rock should keep his wife's name out of his month. 

Pinkett-Smith's hair style has a sad tale behind it. The actress has revealed that she is suffering from alopecia, an autoimmune disease that causes hair to fall out.

In December she posted a video on Instagram explaining why she had shaven her head, saying: “Me and this alopecia are going to be friends ... period!”

The condition results in hair loss on the scalp and in some cases also loss of body hair. 

According to the US National Institute of Arthritis, Musculoskeletal and Skin Diseases, the disease “happens when the immune system attacks hair follicles and causes hair loss”. 

“The course of alopecia areata varies from person to person. Some have bouts of hair loss throughout their lives while others only have one episode. Recovery is unpredictable, with hair growing back fully in some people but not others.

“There is no cure for alopecia areata, but there are treatments that help hair grow back more quickly,” the institute says on its website. 

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