There can be many reasons for this. It could be due to he­at, sweat, or friction. Skin usually rubs against each other whe you walk or do any activity, and wearing tight clothes can further increase friction. Wearing loose clothing can help this problem. You should also keep yourse­lf dry and use mild soap and pat dry your thighs after taking a bath. But if the itchine­ss and redness don't go away, talk to a dermatologist.