What Do Red Rashes On The Legs Indicate?

my adult son has a rash covering both legs. He is 33 years old. we suspect using a new detergent with scent. He wore clothing washed in this new detergent for a week while rash worsened. His legs are very red and burn. My son just used an over the counter hydro cortisone cream and it made the rash burn more than before. Is this just the heat coming out of the rash? would an ice pack such as frozen peas over a cloth help? YYYY@YYYY I forgot to mention. He was exposed to someone with H1N1 flu but has only had a mild respiratory issue.