I always try to wash new clothes before I wear them. Mainly, out of fear that other people tried them on first. But sometimes, whether I get lazy or of I’m in a rush, I’ll wear something without giving it a good cleaning first. Apparently, that’s not the best idea. Dermatologists say you should always wash new clothes, because they can contain chemicals that can seriously irritate your skin.

“I definitely wash all my clothes before wearing them,” says California-based dermatologist Shirley Chi, MD. “I am really careful to wash my kids’ new clothes, too, since their skin is even more sensitive to irritation from chemicals.”

Dr. Chi explains that wearing new clothes without washing them can lead to contact dermatitis, a reaction that occurs when is a your skin is sensitive to, or allergic something that it comes in contact with.  Time reports that contact dermatitis can be the result of disperse dyes, which are used to color synthetic clothing materials like polyester and nylon. Dr. Chi says that it can also be caused by preservatives like formaldehyde, which is used to keep clothes wrinkle-free during shipment.

You should wash your clothes (as well as bed sheets and bath towels) at least once to get rid of most of the chemicals. Some chemical residue will linger, but it should dissipate with subsequent washes. If you have sensitive skin, an ultra-clean natural detergent is best.

If you skip the wash and develop contact dermatitis, Rebecca Baxt, MD, MBA, FAAD, a New Jersey-based dermatologist, says your skin will get red, itchy, and sometimes flaky. If very severe, she says it can even be blistered. Dr. Chi explains that the rash will occur where the clothing touches the skin.

“Often it’s around the armpit,” says Dr. Chi. “And it’s not in the middle of the armpit, it’s around the edge.” Other common sites include around your waist and thighs (“wherever the clothing is tighter”).

Treatment options for contact dermatitis include over-the-counter cortisone creams (Dr. Baxt notes that prescription creams are stronger), antihistamines, and cold compresses.

Two factors that play a role into whether or not you develop contact dermatitis include how log you wear the item, and if you get sweaty, explains Dr. Chi. So you’ll have a lesser chance of getting a rash from wearing a straight-off-the-rack blouse for an hour than you would from wearing a new, unwashed sweater all day, or leggings you bought on the way to the gym.

“If you get sweaty, it releases the chemicals and then is more likely to cause a rash,” says Dr. Chi. “And then you go into the gym or something and next thing you know you have a rash on your thighs.”

OUCH! Okay, so trying my hardest to always wash new clothes before I wear them.

Feel like your workout clothes irritate your skin? Here’s how to make sure they get squeaky clean, and how to tell if you’re actually just allergic to them.