What could cause hair loss?

I am a 20 year old female and i have just noticed a large bald patch on the side of my head.Its not from a scar and is about an inch in diameter. What could have caused this?What could cause hair loss?
Go to your doctor or dermatologist. They should run several blood test. Causes: thyroid, not eatting properly, unknowingly pulling it out, stress, recent surgery?, recently having a baby. God bless you honey. I hope they figure it out for you. Unfortunately, some women have female pattern baldness. Its called alopecia. There is nothing they can do for that. I would definitely make an appointment right away and if your not happy with what they say, see a dermatologist. I hope everything works out for you.What could cause hair loss?
thyroid hormone go to your doctor and get your blood checked for a ';low thyroid hormone level';

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