Sure, some allergic reactions are just a nuisance (*cough* — or should I say *sneeze*? — seasonal allergies).

But, other allergic reactions can be flat-out scary. From facial swelling to a rash covering your entire body, allergic reactions come in all sorts of concerning shapes and sizes.

And when your body goes from totally normal one minute to eliciting wide-eyed reactions from everyone around you the next, it's understandable to panic. How do you know if your allergic reaction is serious enough to warrant a trip to the emergency room? And how do you know if it's safe to just wait it out at home?

"As far as allergic reactions are concerned, most people are probably pretty comfortable self-managing seasonal allergies at home. However, there are a few other types of allergic reactions that — while less common — can be more concerning than your run-of-the-mill, runny-nose-inducing allergies," says Dr. Natalie Dryden, primary care physician at Houston Methodist.

Four commonly encountered allergic reactions are:

1. Allergic rhinitis (aka "allergies")
2. Drug allergies
3. Food allergies
4. Insect sting allergies
   
   

"While allergic reactions can manifest with some pretty uncomfortable symptoms, they're often not a serious medical concern. However, in some cases, they shouldn't be brushed off," warns Dr. Dryden.

That's because some types of allergic reactions can trigger anaphylaxis — a life-threatening emergency that requires immediate medical attention.

"Knowing the types of allergic reactions, what each looks and feels like and the signs that indicate a reaction is serious, can help you decide when to worry and when to self-treat at home," says Dr. Dryden.

Why allergic reactions happen

The primary job of your immune system is to protect you from harmful things that shouldn't be in your body, like viruses and bacteria.

But, sometimes, your immune system is a bit too eager, reacting to something that — sure, is strange — but isn't actually harmful. The result? An allergic reaction.

"Even if you consider something to be familiar, your immune system might not. And it responds by creating molecules called IgE antibodies. These antibodies are built to recognize a particular foreign substance and — when they do — they trigger the complex cascade of events that result in what we know as an allergic reaction," explains Dr. Dryden.

When your body overreacts to something to cause an allergic reaction, the substance is called an allergen. And — in addition to the common ones, like pollen and pet dander — an allergen can be something as desirable as a piece of food, as well as something as unwanted as the venom found in a wasp sting.

Common allergens that cause allergic reactions include:

• Airborne substances: dust, pet dander, pollen and mold/mildew
• Food: eggs, milk, peanuts, shellfish, wheat, fish and tree nuts
• Insect venom: bee and wasp stings
• Medications, including penicillin, and materials, such as latex
  
  

"It's still largely unknown why some substances are more likely to cause allergic reactions than others, as well as why some people overreact to a certain substance but other people don't," says Dr. Dryden. "In addition, the severity of the reaction to a particular allergen can vary from person to person."

And once you have an allergy, it's common for that allergy to remain for life. That's because the allergen-specific antibodies you create stay ready in your body, on high alert for future encounters.

"The one exception to this is a penicillin allergy. Studies have shown that 90% of people who had a milder reaction to penicillin — a rash, for instance — during childhood may no longer be allergic to this drug as an adult," explains Dr. Dryden. "In these cases, it's very much worth having allergy testing done to determine whether you're still allergic to penicillin or not. However, if your reaction to penicillin was more serious, such as anaphylaxis, you will likely be allergic for life."

In addition, Dr. Dryden says that childhood food allergies are sometimes outgrown — but this usually happens by age 16, or not at all.

"A person can also suddenly develop a new allergy as an adult, and this is particularly common with allergic rhinitis and food allergies," adds Dr. Dryden.

What an allergic reaction looks like

Given that there are several types of allergic reactions, it probably doesn't come as much of a surprise that each allergic reaction can look and feel a bit different.

"Allergic reactions can manifest with a variety of unpleasant, and sometimes concerning, symptoms and side effects. These reactions can also affect various areas of your body, including your skin, nose, throat, stomach, ears and lungs," explains Dr. Dryden. "Knowing the distinct signs and symptoms to watch for is the first step in determining how serious your allergic reaction is."

Seasonal allergy symptoms include:

• A runny (or congested) nose
• Sneezing
• Itchy, watery eyes
  
  

Drug allergy symptoms include:

• Raised, itchy, red welts on your skin (hives)
• Swelling in your face
• Wheezing
• Shortness of breath
  
  

Food allergy symptoms include:

• Swelling of your tongue, lips, face or throat
• A tingling sensation inside your mouth
• Raised, itchy, red welts on your skin (hives)
• Shortness of breath and/or throat constriction
  
  

Symptoms of an insect sting allergy include:

• Itching all over your body
• Raised, itchy, red welts on your skin (hives)
• Swelling at the location of the insect sting*
• Wheezing and/or cough
• Chest tightness and/or trouble breathing
  
  

*In the case of an insect sting, local redness and swelling at the site of the bite is normal, and not considered a true allergic reaction unless one or more other symptoms are present.

"If your allergic reaction is mild, you can self-treat your symptoms at home. For instance, over-the-counter antihistamines and creams can be used to reduce seasonal allergies, mild swelling and hives," says Dr. Dryden. "For more troublesome symptoms, you may benefit from an appointment with your primary care physician or an allergist. In addition, some symptoms, such as wheezing, chest tightness and shortness of breath, are more concerning and may warrant a trip to the emergency room."

Most importantly, though, Dr. Dryden says it's vital to monitor for worsening symptoms, because severe symptoms of an allergic reaction shouldn't be self-treated at home.

When is an allergic reaction serious?

"Anaphylaxis is a severe reaction to an allergen. Since it can cause your body to go into shock, it's very important to know the signs and symptoms of anaphylaxis and seek immediate medical attention as soon as you suspect it," warns Dr. Dryden.

The signs and symptoms of anaphylaxis include:

• Raised, itchy, red welts on your skin (hives)
• Flushed or pale skin
• Heavy wheezing and severe shortness of breath
• An irregular pulse, weak or rapid
• Feeling dizzy or lightheaded
• Nausea and vomiting
  
  

"If you think you're having an allergic reaction and are experiencing symptoms of anaphylaxis, call 911 immediately," says Dr. Dryden. "If you have access to an EpiPen, you can administer it as you wait for EMS to arrive. But, do not rely solely on an EpiPen to treat your reaction. Seeking medical attention as soon as possible is still paramount."