Your immune system creates antibodies to fight off foreign substances so you don’t get sick. Sometimes your system will identify a substance as harmful, even though it isn’t. When this happens, it’s called an allergic reaction.

These substances (allergens) can be anything from food and medication to environments.

When your body comes in contact with these allergens, it can cause mild symptoms like skin irritation, watery eyes, or sneezing. In some people, allergies can lead to anaphylaxis. Anaphylaxis is a life-threatening condition. It results in shock, a sudden drop in blood pressure, and difficulty breathing. This can lead to respiratory failure and cardiac arrest.

Immediately call 911 or your local emergency services if you or someone you know is experiencing anaphylaxis.

Your body’s allergic reaction depends on what you’re allergic to. Parts of your body that’ll react include your:

Common symptoms

Take a look at the table below to see which symptoms commonly occur for which allergy:

SymptomEnvironmental allergyFood allergyInsect sting allergyDrug allergy
SneezingXX
Runny or stuffy noseX
Skin irritation (itchy, red, peeling)XXXX
Hives XXX
Rash XXX
Trouble breathing X
Nausea or vomiting X
Diarrhea X
Short of breath or wheezingXXXX
Watery and bloodshot eyesX
Swelling around the face or contact area XX
Rapid pulse XX
Dizziness X

The most serious allergic reactions can cause anaphylaxis. This reaction occurs minutes after exposure and, if left untreated, can lead to loss of consciousness, respiratory distress, and cardiac arrest.

Signs of anaphylaxis include:

Get emergency help if you or someone you know is experiencing anaphylaxis, even if symptoms start to improve. Sometimes symptoms can return in a second phase.

What to do when someone is experiencing anaphylaxis

If you’re with someone who’s experiencing anaphylaxis, you should:

  1. Call 911 immediately.
  2. See if they have an epinephrine (adrenaline) auto-injector (EpiPen) and help them, if needed.
  3. Try to keep the person calm.
  4. Help the person lie on their back.
  5. Raise their feet about 12 inches and cover them with a blanket.
  6. Turn them on their side if they’re vomiting or bleeding.
  7. Make sure their clothing is loose so they can breathe.

The sooner the person gets their epinephrine, the better.

Avoid giving oral medications, anything to drink, or lifting their head, especially if they’re having trouble breathing.

Your doctor can prescribe emergency epinephrine. The auto-injector comes with a single dose of medication to inject into your thigh. You’ll want to teach your family and close friends how to inject the epinephrine in case of an emergency.

If the person you’re with isn’t breathing, coughing, or moving, you may need to perform CPR. This can be done even without formal CPR training. CPR involves doing chest presses, about 100 per minute, until help arrives.

If you’re interested in learning CPR, contact the American Heart Association, American Red Cross, or a local first-aid organization for training.

Over-the-counter (OTC) antihistamines and decongestants may relieve minor symptoms of an allergic reaction.

Antihistamines prevent symptoms such as hives by blocking histamine receptors so your body doesn’t react to the allergens. Decongestants help clear your nose and are especially effective for seasonal allergies. But don’t take them for more than three days.

These medications are available in tablets, eye drops, and nasal sprays. Many OTC drugs also cause drowsiness, so avoid taking them before driving or doing work that requires a lot of concentration.

Swelling, redness, and itching may be reduced with ice and topical creams that contain corticosteroids.

Make an appointment with your doctor if OTC drugs don’t work. Call your doctor right away if you have an allergic reaction to the medication.

The best remedies for food allergies usually entail avoiding foods that trigger an allergic reaction. If you accidentally come in contact or eat the food you’re allergic to, OTC drugs can temper the reaction.

However, these drugs only help relieve hives or itching. Oral cromolyn can help your other symptoms. It’s only available by prescription, so talk to your doctor.

You can also treat severe food allergies with epinephrine.

Poisonous plants

According to The Children’s Hospital of Philadelphia, about 7 out of 10 people have an allergic reaction when they touch poison ivy, poison oak, and poison sumac. The sticky substances from these plants, also called urushiol, bind to the skin upon contact.

Symptoms range from mild redness and itching to severe blisters and swelling. Rashes appear anywhere from three hours to a few days after contact and last one to three weeks.

If exposed to poisonous plants, do the following:

  1. Avoid touching other areas of your body, especially your face.
  2. Clean the area with soap and water for at least 10 minutes.
  3. Take a cool bath.
  4. Apply calamine or another anti-itching lotion three to four times a day to relieve itching.
  5. Soothe inflamed areas with oatmeal products or 1 percent hydrocortisone cream.
  6. Wash all clothing and shoes in hot water.

These steps all focus on removing the urushiol from your skin. Severe reactions in children may require a doctor’s visit to prescribe oral steroids or stronger creams to ease symptoms.

See your doctor if you have a high temperature and:

  • the scratching gets worse
  • the rash spreads to sensitive areas, like the eyes or mouth
  • the rash doesn’t improve
  • the rash is tender or has pus and yellow scabs

Despite some claims, there’s no scientific evidence to support that scratching an open wound leads to poison in the bloodstream. The leftover oil (urushiol) only touches the immediate area. Avoid spreading the oil immediately by washing the affected area with soap and water.

Stinging insects

Most people will have a reaction to an insect bite, but the most serious reaction is an allergic one. About 2 million people in the United States are allergic to insect stings, estimates the Cleveland Clinic.

Most common insect stings are from:

  • bees
  • wasps
  • yellow jackets
  • hornets
  • fire ants

Treat insect allergies with these first-aid methods:

  1. Remove the stinger with a straightedge object, like a credit card, using a brushing motion. Avoid pulling or squeezing the stinger. This may release more venom into your body.
  2. Wash the area with soap and water. Apply an antiseptic after washing.
  3. Apply hydrocortisone cream or calamine lotion. Cover the area with a bandage.
  4. If there’s swelling, apply a cold compress to the area.
  5. Take an antihistamine to reduce itching, swelling, and hives.
  6. Take aspirin to relieve pain.

Pregnant women shouldn’t take OTC drugs without getting the OK from their doctor.

Children shouldn’t take aspirin. This is because of the risk of a rare, but fatal, condition called Reye’s syndrome.

Jellyfish stings

If a jellyfish stings you, wash the area with seawater or vinegar for 30 minutes. This will neutralize the jellyfish’s toxin. Apply something cold on the affected area to soothe your skin and lessen pain. Use hydrocortisone cream and an antihistamine to reduce swelling.

The British Red Cross advises that urinating on a jellyfish sting won’t help. In fact, it may actually increase pain.

In most drug allergy cases, your doctor should be able to prescribe an alternative medication. Antihistamines, corticosteroids, or epinephrine may be needed for more serious reactions.

Otherwise, your doctor may recommend a desensitization procedure. This means taking small doses of the medication until your body can handle your dosage.

Once you’ve had an allergic reaction, it’s important to identify the source to avoid future contact. For ingredient-specific allergies, check product ingredients before purchase. Applying lotion before going hiking or camping may help prevent poison ivy from spreading or absorbing into your skin.

The more control you keep over your contact with allergens, the less likely you’ll have an allergic reaction. Make sure your co-workers and friends know about your allergies and where you keep your epinephrine auto-injector. Teaching your friends how to treat an allergic reaction can help save a life.