An allergic reaction happens when the body identifies a normally harmless substance viz. pollen as an invading germ. The immune system produces histamine to fight off the intruder and that chemical causes the symptoms that make people miserable.

There is no pill, shot or surgery that's going to take away allergies completely. Allergic season brings in sneezing, wheezing, coughing, runny noses, itchy eyes and headaches with it. Antihistamines and other treatments can reduce the symptoms -- but there is no cure.
But some preventions can help.

Most Common causes are: -

Dust mites: They live in bedding, upholstery and carpets.

Pollen: Also sometimes called hay fever are caused by the greenish powder produced by plants for fertilization.

Mold: Mold usually grows in bathrooms or damp basements.

Pets: A pet's saliva, produced while licking, dries and a protein in the saliva floats in the air and sticks to fabric or furniture.

Cockroaches: Trigger allergies & asthma with their droppings, saliva or bodies themselves.

Food : Milk, Eggs, Peanuts, Tree nuts (walnuts, cashews, pecans, etc.), Fish, Shellfish, Soy and Wheat.

Insect stings: Around 2 million Americans are allergic to the venom in the stings of bees, wasps, hornets, yellow jackets and fire ants resulting in swelling, dizziness or passing out, drop in BP and even a heart attack.

Medicines: The antibiotic penicillin is the most common drug allergy. Other drug allergens include anti-convulsants such as Dilantin and insulin from both pork and beef sources.

Chemicals: Itchy skin or rashes may be caused by chemicals in everyday things, such as cosmetics, laundry detergents, household cleaners or dyes.

Treatment / Prevention

Unfortunately, there's no cure for allergies. But there are several ways to keep them under control and treat the symptoms.

Avoidance: The first step is determining what exactly you're allergic to and then of course, avoiding that trigger if at all possible.

Medication: (OTC) Over-the-counter & prescription drugs i.e. antihistamines, decongestants or anti-inflammatory medicine can help relieve many symptoms.

Allergy shots: If allergies don't respond to medication, allergy shots (or immuno-therapy) may be taken. Sadly, shots don't work on all people or for all allergies viz. they don't work for food allergies.