Causes and Risk Factors of Allergies

Allergies can be triggered in many ways, and sometimes the cause can be hard to identify. The allergic reaction is provoked by an allergen, which is a substance that should be harmless but your body over-reacts to and produces antibodies to combat it. Allergens can be a variety of different substances including pollen, mold, pet dander, food, medications, insect stings, and metals.

Allergies develop when you are exposed to an allergen and your body's immune cells produce antibodies to it. On first exposure, you don't have a reaction, but in further exposures, the antibodies kick into action. The allergen may be inhaled, consumed, or come in contact with the skin.

During an allergic process, the substance responsible for causing the allergy (allergen) binds to antibodies present on white blood cells in your body, including mast cells and basophils. The cells then release chemicals such as histamine and leukotrienes, resulting in allergic symptoms. Reactions include skin rash, hives, sneezing, runny nose, nausea, diarrhea, or more serious symptoms such as tongue, lip or throat swelling or having an asthma attack. The most serious form of allergic reactions is anaphylaxis, which involves a "whole body" allergic reaction, which can be life-threatening.

The types of symptoms that occur depend on where in the body this reaction takes place. For example, if pollen is inhaled, then nasal allergies may occur. With a food allergen, swallowing the food may result in a whole-body reaction, such as hives or anaphylaxis.

Airborne Allergens

As many as one-third of adults and 40 percent of children have allergic rhinitis due to airborne allergens. The most common ones are:

• Weeds
• Mold
• Dust mites
• Grass
• Pollen
• Pet dander

Foods: Millions of children and adults in the United States have food allergies. When the culprit food is eaten, most allergic reactions occur within minutes. They can produce skin, nasal, and gastrointestinal, and cardiovascular symptoms, as well as anaphylaxis.

Almost 90 percent of all food allergies are related to these eight foods:

• Milk (primarily in infants and small children)
• Egg
• Peanut
• Tree nuts
• Soy
• Wheat
• Fish
• Shellfish

Medications: Hives and swelling suggest an allergic cause of medication reactions. The most common medication allergies are to penicillin and cephalosporin antibiotics. Less common allergies are seen to non-steroidal anti-inflammatory drugs (NSAIDs). Other medications may produce non-allergic reactions.

Insect Stings and Bites: Sometimes people can experience more severe allergic reactions to insect stings and bites. The most common allergic reactions are seen to:

• Bee stings (honeybee, wasp, hornet, yellow jacket)
• Mosquito bites
• Fire ant stings
• Bed bug bites

Contact Allergens: There are many irritating chemicals that can cause a skin reaction, but some set off a true allergic reaction when you come in contact with them. The most common ones are:

• Poison ivy, oak, and sumac
• Nickel
• Makeup and personal care products
• Latex
• Fragrances
• Antibacterial ointments
• Formaldehyde
• Hair dye
• Leather tanning chemicals

Allergies tend to run in families. You are more at risk if your family history includes people with allergies. This is called being atopic. Your body is more likely than most to see a new allergen as a threat and produce IgE antibodies, which are the ones involved in the allergic response.

Research is actively underway to identify which genes are responsible for making people more susceptible to allergic diseases. But your genes alone might not determine whether you get allergies, as the environment and when you are exposed to allergens may play a big role.

If you are having allergy symptoms, it can be helpful if you can give a good family history to your doctor. Include details of family members who had asthma, hay fever, seasonal allergies, hives, eczema, or severe reactions to insect bites or bee stings.

There are theories that early exposure in infancy to allergens (such as having a dog in the house) and respiratory infections can help prevent developing allergies. On the other hand, the thinking is that it is good to reduce exposure to dust mites by using allergen-impermeable covers on children's bedding and taking other measures to keep their bedrooms free of dust.

Mothers who smoke during pregnancy are more likely to increase the child's risk of allergies. Secondhand smoke also raises the allergy risk for children and infants.

Breastfeeding is recommended for infants for numerous reasons, including reducing the risks of allergies and preventing cow's milk allergies. The mother does not need to avoid any particular foods while breastfeeding.

If you have allergies, avoiding the allergens that trigger them is the key step to preventing allergic reactions. This may mean avoiding outdoor exposure during high pollen seasons, checking carefully for ingredients that can trigger food allergies, and not wearing jewelry that can set off nickel allergies.

A Word From Verywell

The list of what can trigger an allergy is very long. If you are prone to allergies or have a family history of susceptibility, discuss any allergy symptoms you have with your doctor. If you have children or plan to have children, talk to your doctor about the current thinking on allergen exposure and what to look for if you think your child has allergies. Early treatment, especially for children, may reduce the impact allergies will have on their lives.