During hot days, your skin can rebel in other ways too. "Heat and humidity can leave you prone to heat rash," Dr. Berson says. It consists of small, itchy red bumps -- often called prickly heat -- that develop wherever you have tight clothing or friction. Common areas include beneath or between the breasts, on the neck, or under the arms. To prevent the rash, keep skin dry and wear loose-fitting clothes made of breathable fabrics such as cotton. If your skin becomes really itchy, you may want to apply a 1 percent hydrocortisone cream, Dr. Berson says.