My friend has pimples on her bottom and at the tops of her legs under her bottom she's not fat
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it usually has nothing to do with weight...acne on your back, butt or upper legs is called joggers acne and could be one of several things....they may be having a reaction to soap, laundry detergent or dryer sheets...sometimes frictioon from clothes is all it takes, especially if you are hormonal or a teenager. she may also not be getting enough water. another way to get it is to have a skin condition known as cysytic acne, which will require a dermatologists care...she should also try a gentle exfoliating technique...good luck