Prickly heat comes out when sweat is not able to evaporate from skin due to chafing or tight clothing. the sweat glands become blocked and can result in areas of pink irritated skin that may be dotted with red bumps.
It would be best to wear loose breathable clothing and change out of sweaty items as soon as possible to avoid having prickly heat. If you already have it, soothe affected area with aloe vera gel and ease itching with a cortisone cream. The red bumps will clear up in about a week.