Most people associate hives — the raised, puffy welts on your skin that spread when scratched — with an allergic reaction, but there are a number of factors that can cause them. One of these factors is stress, and if you find yourself breaking out in hives without another likely cause, it’s possible that stress is to blame. We spoke to Mary Stevenson, an assistant professor of dermatology at NYU Langone, to learn more about what causes stress hives, and what to do — and what not to do — if you have them.

What do stress hives look like?
Stress hives can look a little like bug bites: both are red, puffy, and itchy, and may appear initially as individual bumps, says Stevenson. However, hives are more often irregular in shape and can join together in larger patches, especially if you scratch them. A bad case of hives may appear as a single large patch of puffy, raised skin.

What’s the difference between stress hives and a stress rash?
Though “rash” is a commonly used colloquial term, dermatologists don’t really use it descriptively, says Stevenson. If you have an area of skin covered in small, irritated, red papules, or bumps, you might be more likely to call that a rash, but Stevenson says these conditions — rashes and hives — are two points along the same spectrum. “Some people, when they’re stressed out, notice that their skin gets red or itchy, and the more extreme end is that they’re not only itchy and red, but they’re having hives,” she explains. If you already have a skin condition, like psoriasis, eczema, or acne, stress can definitely make those conditions worse. Stress affects different people’s skin in different ways.

Why do I have hives?
If you’re noticing hives or a rashlike reaction, it’s wise to do a survey of your last few days to look for possible causes before deciding stress is to blame, says Stevenson. “Maybe you changed your laundry detergent that week, or you ate all these new foods or started a new medication,” she says. Unlike stress, many of these are factors that can be easily eliminated.

If none of the above apply, and you’re feeling more pressure than usual, it’s very possible stress is responsible for your hives. Most at-risk for stress hives are women in their 30s and 40s who have previously experienced hives for another reason. When our sympathetic nervous system is “revved up,” says Stevenson, it causes histamine release, which causes hives. Histamine is a compound released by cells in response to injury, and in allergic and inflammatory reactions.

What happens if I scratch my hives?
Don’t do that. When you scratch your hives, you cause more histamine to release, which — you guessed it — creates more hives. This starts a vicious cycle. “The more you scratch, the more you itch, the more you itch, the more you scratch,” says Stevenson. “It’s the same advice I’d give about popping a pimple: keep your paws off.”

How long do stress hives last?
Most hives should be gone within 24 hours, says Stevenson, but that’s not to say that new welts can’t be formed, particularly if the causal factor is still at play. If you’re treating your hives (more on that in a minute), and you haven’t seen improvement in a few days, Stevenson recommends making an appointment with a dermatologist.

How should I treat stress hives?
As is often the case, the best treatment is prevention, though it’s obviously not always possible to prevent oneself from feeling stressed. Stevenson acknowledges that being told to “relax” is unlikely to help matters, and may exacerbate the problem. “De-stressing is hard,” she says, but if there are ways to reduce stress in your daily life, doing so will positively impact your health.

If you’re breaking out in hives, it’s a good idea to take an antihistamine, like Claritin or Allegra, to help block the histamine pathway from forming new hives. (You can also take Benadryl, but it’ll most likely knock you out, so it’s probably best to save that for nighttime.) Stevenson says you want to do this as long as your symptoms last, and for a couple of days after the hives are gone, too.

You can also treat hives topically, to help minimize the itching. Applying a cold compress can help reduce itching as well as swelling, as can topical steroids like Hydrocortisone. Some people find milk compresses helpful, says Stevenson, because the fat in whole milk (skim won’t work here) can soothe irritated skin. And again, if those things aren’t helping after a few days, call your dermatologist. “We can use different medications and different doses to help get things under control,” says Stevenson.