Causes and Risk Factors of Allergies
Your risk of developing allergies is higher if you:
- Have asthma
- Have a family history of asthma or allergies
- Are younger than 18
Children sometimes outgrow allergies as they get older. It’s also not uncommon for allergies to go away and then return years later.
You may have more than one allergy. Children with food allergies, for instance, are as much as four times more likely to have other allergic conditions, including asthma, than those without food allergies.
More than 100 genes are associated with allergies, although only one or two genes affect any given population. Some of these genes affect the immune response; others affect lung and airway function.
Allergic Reactions
Allergens are typically harmless substances that trigger an immune response and cause a reaction in people who are allergic. The allergic reaction occurs if the person inhales, touches, swallows, injects, or somehow comes into contact with the allergen. Allergic reactions can be mild, severe, or even life-threatening.
Normally, the immune system protects the body against harmful substances, such as viruses or bacteria. If you have allergies, “your body responds to allergens as if they were invaders,” explains Clifford Bassett, MD, a clinical assistant professor at New York UniversityLangone Health in New York City. “Your body exaggerates the immune response. That’s what causes histamine release and other things that cause allergy misery.”
Histamine also acts as a neurotransmitter in the brain, sending messages between cells. It plays a key role in many different physiological functions, such as telling your stomach to produce acid to digest food or helping regulate your sleep-wake cycle.
When your immune system reacts to an allergen, it produces an antibody called immunoglobulin E (IgE). The production of IgE is part of your body’s attempt to destroy the allergen and protect itself. Your blood vessels dilate and become leaky, so white blood cells that fight infection and other protective substances leave the blood vessels to attack the invader.
In the process, the IgE antibodies signal other cells to release certain chemicals, such as histamine, in the local tissue and blood stream. Too much histamine or excessive release in the body can cause an unwanted response that leads to skin, nose, throat, and lung irritation or more severe symptoms of anaphylaxis.
In this way, a normally protective process creates a cascade of what we know as allergy symptoms in response to harmless allergens.
There are other types of allergic reactions, such as delayed hypersensitivity reactions, which includes contact dermatitis from poison ivy or a nickel allergy — these are mediated by T cells in the immune system rather than antibodies.
The most common allergens that trigger allergic reactions include:
- Pollen
- Dust mites
- Pet dander or fur
- co*ckroaches
- Mold spores
- Foods (eggs, fish, milk, peanuts, tree nuts, wheat, soy, shellfish, and others)
- Insect stings or bites (from wasps, bees, mosquitoes, fire ants, fleas, horseflies, black flies, among others)
- Medicines, such as penicillin, aspirin (Vazalore), and others
- Latex
- Household chemicals
- Metals (especially nickel, cobalt, and chromates)
Seasonal Allergies
Certain allergies can strike at any time of year. Seasonal allergies, on the other hand, occur at times of the year when certain types of outdoor allergens are predominant.
“You can have both,” says Dr.Bassett.
And about two-thirds of people with seasonal allergies actually have year-round or persistent allergies.
Seasonal allergies are most often triggered by outdoor molds and pollen from trees, grasses, and weeds, such as ragweed. The allergic reaction occurs during the weeks or months when the plant pollinates.
Allergy triggers may vary depending on geographic location and climate, but relocating to avoid seasonal allergies generally doesn’t help. Pollen and mold spores travel great distances, and people with allergies often develop sensitivity to other allergens in a different location.
Environmental factors, such as pollution and climate change associated with rising temperatures, may be contributing to a rise in allergies. Changes in the duration and intensity of pollen and mold seasons mean more people are exposed to allergens for longer amounts of time. “That’s a longer period of time for your eyes and nose and throat to become symptomatic as a result,”Bassett says.
In a 2015 survey of allergists, 63 percent of respondents felt climate change was causing an increase in allergic symptoms among their patients.
