Itchy bumps and painful blisters can ruin your warm-weather plans whether you’re in the woods wearing your hiking treads thin or on the patio barbequing on a new kickass grill.

But they don't have to. Enter our guide to all things summer rash-related. This rundown can help you identify and treat skin problems like poison ivy, heat rash, and chigger bites—as well as fend off future run-ins.

But before you self-diagnose, remember this: While summer rashes will usually clear up with an over-the-counter cream, skin infections that come with a fever, headache, shortness of breath, or abdominal pain require a trip to the doc, warns Lewis Nelson, M.D., a New York City-based emergency medicine doctor and medical toxicologist.

1. Heat rash (aka prickly heat)

What it looks like: Small zit-like bumps on the back and chest, or deep, painful, acne-like breakouts in more severe cases.

Causes: Excessive sweating in hot, humid weather can clog pores and cause breakouts.

How to treat it: Use an anti-itch cream with a combo of camphor and menthol, like Sarna Original Lotion, calamine lotion, or 1% hydrocortisone cream to help relieve discomfort. Otherwise, you need to wait for the pores to open up on their own for the rash to go away.

See a doc if: You’re still itching after a week or if the rash doesn’t go away on its own. A physician may prescribe a stronger cortisone cream or an anti-acne medication to exfoliate skin and open pores.

Your best defense: Be mindful when you know you’re going to sweat. Skip heavy moisturizers, pick oil-free, non-comedogenic sunscreen, and wear loose-fitting clothing instead of sweat-trapping spandex.

2. Swimmer’s itch

What it looks like: Small, red, very itchy bumps or blisters that may also burn.

Causes: Swimmer’s itch is actually an allergic reaction to a parasite found in open water. It burrows into skin and causes an inflammatory reaction.

How to treat it: Use anti-itch cream, 1% hydrocortisone cream, or an antihistamine to stop the itch. Colloidal oatmeal or baking soda baths can also soothe skin.

See a doc if: Symptoms don’t disappear after a week.

Your best defense: If you’ve been in infested water, towel off after swimming to decrease your chances of developing the itch.

 

3. Poison ivy, oak, and sumac

What it looks like: Tiny fluid-filled blisters in a linear or crisscross pattern.

Causes: Direct contact with poison ivy, poison oak, or poison sumac. All three plants contain the toxin urushiol, which most people are allergic to. If you’ve been exposed before, you’ll likely notice the rash within 48 hours, but blisters can take up to 10 days to appear if it’s your first encounter, says Nelson.

How to treat it: For mild cases, OTC calamine lotion should control itching. In more severe cases, use an antihistamine. Go for a topical cream if the rash is contained, and for more spread-out rashes use an oral diphenhydramine, like Benadryl Allergy tablets, non-drowsy Zyrtec, or Claritin. Still scratching? Hydrocortisone cream packs the strongest punch by reducing the inflammation that’s causing the itch.

See a doc if: The OTC lineup doesn’t kick the itch within a week (the irritation should subside in about three to five days), or if the rash lingers past a couple of weeks.

Your best defense: First off, follow the old adage, “Leaves of three, let it be.” If you suspect you’ve been exposed, wash the area with soap and water within 15 minutes of contact—you may be able to avoid catching a rash. And beware: Clothing, garden tools, or even pets that have been exposed to poison ivy, oak or sumac, can spread the toxin.

4. Ragweed

What it looks like: Small, itchy bumps and blisters, and hives in severe cases. Your rash will likely be accompanied by a runny nose, itchy throat, and dry, scratchy eyes.

Causes: A ragweed-triggered rash is an allergic reaction to the pollen in the plant.

How to treat it: Oral antihistamines will help relieve itchy skin and irritated eyes, nose, and throat.

See a doc if: Symptoms persist even after an OTC regimen, or if you develop a fever, shortness of breath, or abdominal pain.

Your best defense: The less pollen you’re exposed to, the better—easier said than done when you’re outdoors during the summer months. If you’re overly sensitive, ask your doctor about cromolyn, a nasal spray that may thwart your over-the-top reaction.

 

5. Lyme disease

What it looks like: A small, red bump that grows into a large, plastic-feeling bull’s-eye after a few days.

Causes: A tick latches onto your skin and transfers harmful bacteria to you. You’ll notice the bite right away, and the disease can follow.

How to treat it: You'll likely need an antibiotic, which will kill the infection, though the rash may take several days to clear up.

See a doc if: As soon as you suspect you’ve been infected or if you notice a tick, see your doctor. Untreated Lyme disease can lead to serious complications in the heart and joints.

Your best defense: Wear long pants and long sleeves if you plan to be in a wooded area. Also use a DEET-based insect repellent, advises Donald Belsito, M.D., a New York City-based dermatologist. If you find a tick on your skin, remove it soon as possible. (After a tick attaches to your skin, it takes 36 to 48 hours for the insect to infect you.) Use tweezers to grab it as close to the skin’s surface as possible. Be sure to remove the whole tick, then wash the area thoroughly.

6. Sun allergies (aka photosensitivities)

What it looks like: A red, scaly, and extremely itchy allergic reaction that’s sometimes accompanied by tiny water blisters.

Causes: Sun exposure triggers an allergic reaction to certain chemicals, like those founds in medications, in the body. A similar allergy—polymorphous light eruption—is caused by a direct sensitivity to the sun’s UVA rays, and according to dermatologists, your genetics are probably to blame.

How to treat it: Oral antihistamines and anti-itch creams will help relieve symptoms, but if you suspect you have a sun allergy, getting the right diagnosis from your doctor can help you avoid the allergy triggers in the future. PMLE may require stronger prescription medication.

See a doc if: Symptoms don’t go away within a week. You likely need a stronger, prescription-strength cream (or for extreme cases, an oral steroid, like prednisone).

Your best defense: Though your doctor or pharmacist should warn you if a prescription drug can cause a sun allergy, keep an eye out for these common culprits: ketoprofen (found in some prescription pain meds) or tetracycline, doxycycline, or minocycline (all found in antibiotics). And, of course, lather on the broad-spectrum SPF.
 

7. Athlete’s foot

What it looks like: Cracking, itching, or skin that looks white, dry, scaly, or pruney.

Causes: Going barefoot in environments where fungi thrive, like pools, the backyard, or the gym.

How to treat it: An OTC antifungal medication, like Micatin, should tackle the infection within a few weeks. Until it clears, be sure to keep skin dry so fungus doesn’t spread. Also avoid wearing shoes without socks, and try not to wear the same shoes two days in a row, as fungus can get in the lining of shoes and re-infect skin.

See a doc if: Skin hasn’t cleared within three to four weeks, or if you notice symptoms in the nails, too. You may need a prescription-strength medication.

Your best defense: Keep your flip-flops on.

8. Chigger bites

What it looks like: Tiny pink or flesh-colored bumps that itch—a lot.

Causes: Chiggers, small mites that live in tall grass and can latch onto skin, bite and leave behind itchy welts.

How to treat it: OTC anti-itch creams and oral antihistamines usually ease symptoms and help bumps to subside in about a week.

See a doc if: If a week goes by and your OTC regimen hasn’t stopped the itch.

Your best defense: Chiggers tend to be most active during the early evening and nighttime hours, so use DEET-based insect repellent if you’re hitting up a backyard barbecue or going for an after-dinner hike.