Sisters talk about alopecia
Newsround has been to meet two sisters who have a condition called alopecia, which can make you bald.
It can happen to anyone and means your body stops making hair - and the hair you do have can disappear completely.
Sisters Emily, who's 11, and nine-year-old Faye both started losing their hair when they were very young but say it's just normal life for them.
"It's OK having alopecia," said Faye. "It doesn't stop me doing anything I want to do."
Emily said: "Sometimes they'll ask my why am I bald and I'll just tell them about what alopecia is."
And Faye added: "I'm used to people coming up to me - I'm not really bothered what they say."
Medical experts have done lots of research to try to find out why it happens but no-one really knows what causes the condition.
Although it might look or feel strange, people who have it aren't ill.
For about three quarters of people who have alopecia, their hair eventually grows back.
Find out more about alopecia
In the meantime, more's being done to support children with the condition.
Emily and Faye have just got back from the first UK summer camp for children with alopecia, where they could hang out with other people their own age who have the condition.