Jock Itch (Tinea Cruris):
Teen information

Tinea cruris is the medical term for jock itch, which is an itchy fungal infection of the skin of the groin. The rash of jock itch usually begins in the top creases of the thigh as raised, red, itchy patches and may become pink or red, flaky or bumpy as it spreads. The fungus (Trichophyton rubrum) is the same as that which causes other types of ringworm, including athlete's foot, so anyone with any type of ringworm may spread the infection to other areas on the body. 

Jock itch is easily treated, though it is contagious so it is best to avoid intimate contact or sharing of towels or clothes until it has gone away.