What are allergies?
Allergies are your body’s reaction to a foreign protein. Usually, these proteins (allergens) are harmless. However, if you have an allergy to a particular protein, your body’s defense system (immune system) overreacts to its presence in your body.
What is an allergic reaction?
An allergic reaction is the way your body responds to an allergen.
If you have allergies, the first time you encounter a specific allergen, your body responds by creating immunoglobulin E (IgE). Your immune system makes antibodies to form IgE.
IgE antibodies bind to mast cells (allergy cells) that live in your skin, respiratory tract (airways) and the mucus membrane in the hollow organs that connect to each other from your mouth to your anus (gastrointestinal or GI tract).
The antibodies find the allergens in your body and help remove them by taking them to the mast cell (allergy cell), where they attach to a special receptor. This causes the allergy cell to release histamine. Histamine is what causes your allergy symptoms.
How common are allergies?
Allergies are very common.
More than 50 million people in the United States have an allergic reaction each year. They’re the sixth-leading cause of long-term illness in the United States.
Who do allergies affect?
Allergies can affect anyone.
You’re more likely to have or develop allergies if your biological parents have allergies.
Symptoms and Causes
What are the most common allergies?
The most common allergies include:
Food allergies develop when your body releases a specific antibody to a particular food. An allergic reaction occurs within minutes of eating the food, and symptoms can be severe. Symptoms may include:
- Itching all over your body (generalized pruritus).
- Itching in just one certain part of your body (localized pruritus).
- Nausea and vomiting.
- Swelling around your mouth, including your throat, tongue or face.
If you have an IgE-mediated food allergy, symptoms may also include anaphylaxis. It may present as any one of the above symptoms or a combination of the above symptoms. It usually occurs within 30 minutes of ingesting a food you’re allergic to.
In adults, the most common food allergies are:
- Tree nuts.
In children, the most common food allergies are:
- Tree nuts.
Inhalant allergies are airborne substances that you inhale (breathe in). They include allergens that may affect you throughout the year (perennial allergens) and seasonal allergens.
Inhalant allergy symptoms include:
- Runny nose.
- Stuffy nose.
- Itchy nose.
- Itchy eyes.
- Watery eyes.
If you have asthma, inhalant allergies can also trigger or worsen your symptoms, including wheezing and shortness of breath.
Perennial allergens include:
- Pets. Pet allergens include certain proteins in animal fur, skin (dander), urine (pee) and saliva (spit).
- Dust mites. Dust mites are tiny, eight-legged relatives of spiders. They’re too small to see with your eyes. They live in dust and the fibers of household objects, such as pillows, mattresses, carpets and upholstery.
- Cockroaches. Cockroaches are reddish-brown insects that are 1.5 to 2 inches (in) long. The proteins in their feces (poop), spit, eggs and dead body parts can cause allergic reactions.
- Molds. Molds are tiny fungi (plural of fungus). They have spores that float in the air, like pollen. Common mold allergies include Aspergillus, Cladosporium and Alternaria.
Seasonal allergies include pollens. Pollen is microspores from trees, grass or weeds that appear as a fine dust on surfaces or float in the air. Tree pollens generally appear in the spring, while weed pollens generally appear in the fall.
Certain medications can cause an allergic reaction. The medicines may be herbal, over-the-counter (OTC) or prescription.
Common medications that cause allergies include:
- Nonsteroidal anti-inflammatory drugs (NSAIDs).
- Chemotherapy drugs.
- Shortness of breath.
Latex allergies develop after repeated contact with natural rubber latex.
Common natural rubber latex products include:
- Rubber gloves.
- Rubber balls.
The most common reaction to latex is skin irritation (contact dermatitis). It manifests as a rash on the area of skin that touched the latex. It may develop within minutes of exposure to latex. Other symptoms may include:
- Runny nose.
- Itchy nose.
- Difficulty breathing.
Stinging insects can inject venom, which is a toxic substance. The venom in insect stings can cause an allergic reaction. The most common stinging insects that cause allergic reactions include:
- Fire ants.
- Yellow jackets.
Venom symptoms are consistent with anaphylaxis. They may include:
- Difficulty breathing.
- Swelling in your face, mouth or throat.
- Difficulty swallowing.
- Rapid pulse.
- Drop in blood pressure.
Can allergies cause a fever?
No, allergies can’t cause a fever.
What causes allergies?
Allergies develop when your immune system reacts to a foreign substance or protein.
Are allergies contagious?
No, allergies aren’t contagious. You can’t spread your allergies to another person.
Diagnosis and Tests
How are allergies diagnosed?
If you think you have allergies, don’t wait to see if your symptoms go away. If your symptoms last longer than a week or two or tend to come back during certain times of the year, make an appointment with an allergist.
An allergist is a healthcare provider who specializes in allergies. They can help diagnose your allergies through tests.
How do I test for allergies?
There are different types of allergy tests. The most common allergy tests are skin prick tests and blood tests.
Skin prick (scratch) tests can identify the allergens that cause your allergy symptoms. An allergist will use a thin needle to prick your skin with a tiny amount of different possible allergens. They then check to see if your skin reacts to the allergen.
Blood (IgE) tests can also identify allergies. However, they’re not as sensitive as skin prick tests. Blood tests evaluate IgE antibodies that your immune system produces against a specific protein.
Management and Treatment
How are allergies treated?
Avoiding allergens is an important treatment approach. However, it often doesn’t completely end allergic reactions. Over-the-counter and prescription allergy medications are also a solution to managing your allergies. These may include:
- Cetirizine (All Day Allergy-D® or Zyrtec®).
These medications are very effective and safe to use daily but they may take a few days to a week to kick in.
- Fluticasone nasal spray (Flonase® or ClariSpray®).
- Cromolyn sodium.
- Antihistamine nasal sprays
These medications should be used cautiously when treating allergies due to higher side effects and concerns related to long-term use.
- Phenylephrine (Sudafed PE® or Sudogest PE®).
- Pseudoephedrine (Contac® or Sudafed®).
- Inhaled or oral bronchodilators.
- Inhaled steroids.
- Oral antileukotrienes, including montelukast, zafirlukast and zileuton.
- Injected drugs, including omalizumab, dupilumab or benralizumab.
A healthcare provider may recommend immunotherapy (allergy shots) and/or sublingual immunotherapy (allergy drops) if you can’t manage your allergy symptoms through over-the-counter and prescription medications and avoiding allergens. The provider will expose you to small amounts of allergens and gradually increase the dosage over several months. Gradual exposure creates a tolerance to the allergen.
Nasal saline irrigation
A neti pot is an over-the-counter device that pushes a saline (salt) solution through your nasal passages. It helps clear out mucus and allergens trapped inside your nasal passages.
What is the best treatment for allergies?
Nasal steroid sprays are generally the most effective medication for people with allergic rhinitis symptoms. Antihistamines block some of the effects of histamine and may offer additional benefits. Immunotherapy helps create a tolerance to allergens and can improve many of the symptoms related to inhalant allergy exposure.
Remember, your body is unique. What over-the-counter or prescription medications work for one person may not work well for you.
Talk to a healthcare provider. They can help recommend the best treatment for you.
What can/can’t I eat/drink if I have food allergies?
If you have food allergies, avoid any products that contain the allergens. By law, manufacturers must include all ingredients on the label of packaged foods for sale in the United States.
You should also consider other possible food allergy exposures. Some nonfood items may contain food allergens, and labeling laws don’t apply to nonfood items.
During the manufacturing process, some food items share equipment or surfaces. Look for labels that state whether the product shared equipment with possible food allergens.
How can I prevent allergies?
The best way to prevent allergies is to avoid allergens. You can also take antihistamines or other medications daily to help control your symptoms and reduce your allergic reaction.
If you have animal allergies, avoid petting, hugging or kissing animals. Don’t allow them in your bedroom or on your furniture.
Regularly vacuuming rugs, carpets and other surfaces helps remove dust, animal dander, pollen and other allergens.
High-efficiency particulate (HEPA) air filters can also help. These air purifiers remove airborne allergens from your environment.
Outlook / Prognosis
What can I expect if I have allergies?
Living with allergies can be challenging. Symptoms can range from mild to severe. However, with caution, you can lead a fulfilling life. Your healthcare provider can recommend resources, support groups and specialists to help you.
How long can allergies last?
Your allergies will last as long as your allergen exposure. Once you’re no longer around allergens, your symptoms should go away after a few hours. However, if you have inhalant allergies, your symptoms may last for several days or longer due to ongoing exposure to pets, dust mites and pollens.
Can children outgrow allergies?
Yes, some children can outgrow their allergies. However, it depends on the type of allergy and the severity of your child’s allergy.
When should I see my healthcare provider?
Go to the ER or call 911 immediately if you start showing symptoms of anaphylaxis.
What questions should I ask my healthcare provider?
- How can you tell that I have allergies?
- What am I allergic to?
- Do I have mild, moderate or severe allergies?
- What medications do you recommend?
- Should I take allergy medications every day or only when I develop symptoms?
- What’s the complete list of side effects of your recommended allergy medication?
- Can you recommend an allergist?
- Can you recommend a dietitian?
Frequently Asked Questions
What is the difference between a cold and allergies?
A cold is a contagious upper respiratory infection. Viruses cause colds.
Allergies are your immune system’s response to an allergen. Viruses aren’t allergens.
A cold shares many of the same symptoms as allergies. These include sneezing, runny nose, cough and congestion. However, there are differences between cold symptoms and allergy symptoms.
- Mucus. If you have allergies, your mucus is usually clear and watery. If you have a cold, your mucus is generally thicker and discolored (yellow or green).
- Eyes. If you have allergies, your eyes may be itchy, watery or red. These symptoms don’t usually develop if you have a cold.
- Duration. Without treatment, allergy symptoms may last for weeks or months until you’re no longer around the allergen. Cold symptoms usually go away after about 10 days.
A note from Cleveland Clinic
Allergies occur when your immune system mistakenly triggers an allergic reaction to an allergen. Allergic reaction symptoms include congestion, watery eyes, a runny nose, vomiting and, in severe cases, anaphylaxis.
Allergies can be incredibly frustrating if you don’t know what’s triggering your immune system. However, a healthcare provider can help provide relief. They can conduct tests to pinpoint your allergies and prescribe medications. They can also refer you to specialists or support groups.