If my upper leg is itchy, how do i know if it is a fungus and should treat like that or a rash and treat with cortisone?

Itchy rash in groin: The site of the lesion makes me suspect-- ' jock itch' which is a fungal infection. Need to see your pcp to make the right diagnosis. Remember using steroids on fungal infection can make it worst.

Difficult to say…: Without seeing the rash or knowing its location fungus (tinea) would tend to affect groin, both sides, unless rash is circular in shape w/ raised edge & more normal center (ringworm) does rash have blisters (like poison ivy) or just flat? Any metal/rubber contact with rash area (contact dermatitis). Have fp take a look at it to get better idea what cause might be.