Acne originates in the pores in the skin, with the pores in the thigh containing cells that produce hair and glands that secrete sebum. These pores get clogged with dirt, oil and bacteria, with tight pants and shorts made of synthetic fabrics rubbing against the thighs and also prohibiting effective breathing of the skin. In addition sweating quite common in the thighs could combine with the oils, dirt and bacteria and clog pores and cause acne breakouts.
Acne can also appear when the skin on the thighs rubs against each other, with oil based moisturizers causing breakouts. Next exercise with sweating in the thighs and use of stretching and yoga mats made of material that clog pores could aggravate acne conditions. Most importantly, hormones can trigger sebaceous glands especially during stress, menstruation and pregnancy and cause increased acne in the thighs.