آلرژی Allergy

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.

Common allergens include pollen and certain food.Metals and other substances may also cause problems.Food, insect stings, and medications are common causes of severe reactions.Their development is due to both genetic and environmental factors.The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.Diagnosis is typically based on a person's medical history. Further testing of the skin or blood may be useful in certain cases.Positive tests, however, may not mean there is a significant allergy to the substance in question.

Early exposure to potential allergens may be protective.Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines.In severe reactions injectable adrenaline (epinephrine) is recommended.Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites.Its use in food allergies is unclear.

Allergies are common.In the developed world, about 20% of people are affected by allergic rhinitis,about 6% of people have at least one food allergy, and about 20% have atopic dermatitis at some point in time.Depending on the country about 1–18% of people have asthma.Anaphylaxis occurs in between 0.05–2% of people.Rates of many allergic diseases appear to be increasing.The word "allergy" was first used by Clemens von Pirquet in 1906.[1]

Symptoms & Types [2]
Learn the types of allergies including food allergies, seasonal allergies, pet allergies, and many more.

Respiratory Allergies
   - Spring Allergies
  There's no cure but you can take steps to curb springtime allergies, from medication to  household habits.
   - Summer Allergies
Summer allergies are usually triggered by pollen from grasses and weeds.
   - Fall Allergies
Ragweed, mold and dust mites are the biggest allergy triggers in the fall.
   - Winter Allergies
If you have indoor allergies such as mold and dust mites, you may notice symptoms more during winter, when you spend more time inside.
Hay Fever
Hay fever, also known as allergic rhinitis, is an immune disorder characterized by an allergic response to pollen grains and other substances. There are two types: seasonal, which occurs only during the time of year in which certain plants pollinate, and perennial, which occurs year-round.
Pollen Allergies
More than 25 million Americans are allergic to pollen from trees, grass, or weeds.
Mold Allergy
All of us are exposed to some mold every day, and usually, there are no problems. But if you have allergies to it, you can have a reaction if you’re around too much of it
Dust Allergy
For creatures you can't even see, dust mites can stir up a lot of trouble.
Dog Allergy
For a person with dog allergies, life in a dog-loving country isn't easy. Approximately 37%-47% of American households have a dog.
Cat Allergy
About 10% of the U.S. population has pet allergies and cats are among the most common culprits. Cat allergies are twice as common as dog allergies.
Food Allergies
Is It an Allergy or an Intolerance?
Food allergies or food intolerances affect nearly everyone at some point. People often have an unpleasant reaction to something they ate and wonder if they have a food allergy.
Milk Allergy
If you suffer from a milk allergy, strictly avoiding milk and food containing milk and milk products is the only way to prevent a reaction, which can include immediate wheezing, vomiting, and hives.
Casein Allergy
If a glass of milk or slice of pizza causes swollen lips, hives, or other symptoms, you may have an allergy to casein, a protein in milk. Another milk protein associated with allergies is whey. Some people are allergic to both casein and whey.
Egg Allergy
Egg allergies are more common in children than in adults. Reactions range from mild to severe.
Wheat Allergy
It can be a challenge to avoid wheat because it’s in so many things.
Nut Allergy
If you suffer from a nut allergy, strictly avoiding nuts, including peanuts and tree nuts like cashews and walnuts, and food containing nuts is the only way to prevent a reaction.
Fish Allergy
If you’re allergic to one kind of fish, your doctor may have told you to avoid others. Here’s what to look out for.
Shellfish Allergy
If you re allergic to one type of shellfish, you may have problems with others. Take these steps to make sure you don’t have an allergic reaction.
Sulfite Sensitivity
Sulfites are a group of sulfur-based compounds that may occur naturally or may be added to food as an enhancer and preservative. The FDA estimates that one out of 100 people is sensitive to the compounds.
Soy Allergy
If all you needed to do for a soy allergy was skip the soy sauce and tofu, life would be a breeze! But soybeans are a big part of processed foods, too.
Skin Allergies
Contact Dermatitis
Something touches your skin, and your immune system thinks it's under attack. It overreacts and sends antibodies to help fight the invader, called an allergen. The result is a red, itchy rash where the substance landed.
Hives (Urticaria) and Angioedema
Hives, also known as urticaria, are an outbreak of swollen, pale red bumps, patches, or welts on the skin that appear suddenly -- as a result of allergies, or for other reasons. In angioedema, the swelling happens under the skin, not on the surface.
Allergies to Poison Ivy, Oak, and Sumac
Poison ivy, poison oak, and poison sumac are plants that contain an irritating, oily sap called urushiol. Urushiol triggers an allergic reaction when it comes into contact with skin, resulting in an itchy rash, which can appear within hours of exposure or up to several days later.
Allergies to Insect Stings
Bee, wasp, yellow jacket, hornet, or fire ant stings are the insect stings that most often trigger allergies. Most people are not allergic to insect stings and may mistake a normal sting reaction for an allergic reaction.
Can You Be Allergic to the Sun?
Most people's skin will burn if there is enough exposure to ultraviolet radiation. However, some people burn particularly easily or develop exaggerated skin reactions to sunlight.
Cosmetic Allergies
Some beauty products can cause skin irritation or allergic reactions. Certain ingredients used in cosmetics, such as fragrances and preservatives, can act as allergens, substances that trigger an allergic reaction.
Nickel Allergy
A nickel allergy is a skin reaction that develops after exposure to nickel or items containing the metal.
Other Allergies
Eye Allergies
Millions of Americans have allergies. Most of those millions have symptoms involving their eyes.
Allergic Conjunctivitis (Pink Eye)
Conjunctivitis is one of the most common and treatable eye conditions in children and adults.
Drug Allergies
Many medications can cause side effects, and certain ones can trigger allergies.
Aspirin (Salicylate) Allergy
If you're allergic to chemicals called salicylates, you may need to avoid certain foods, medicines, and other products.
Penicillin Allergy
Since the 1940s, penicillin has been a go-to drug to clear up infections caused by bacteria. But some people get a bad reaction from taking it.

image: collierotolaryngology.com/allergy-symptoms

Reference: 1.en.wikipedia.org 2.webmd.com