Bumps that suddenly develop in
the face or the body may be due to hives, a skin
reaction to allergen, medication or infection. They are pink to red bumps or slightly raised patches of skin which may last for a few minutes or hours. In this condition, it is important to determine and avoid the trigger that could be causing this. Are there other symptoms present? Since the location is at her back, buttocks and thighs, it may also be due to an irritation or possible allergic reaction.