Spring is right around the corner and it’s time to get ready for warmer weather. Most people will take out their windbreakers, sneakers and short-sleeved shirts. More than 9 million Americans will also take out their seasonal allergy medication, according to the University of Chicago Medical center.

Every year, the onset of spring signals the pollination of trees and grass. This pollination triggers a response in many individuals that leads to a runny nose, sneezing and watery eyes — classic signs of allergies.

Allergic rhinitis, commonly known as seasonal allergies or hay fever, is caused when membrane lining, such as that in the nasal passages, comes in contact with a natural molecule, such as pollen, that produces a negative reaction in the body. Histamine is released by the immune system and skin can redden as blood vessels dilate, explained Dr. James Thompson, board-certified allergy and asthma specialist in Chicago.

“The mucus glands are overactive, causing a running nose … or post-nasal drip in the throat, which can lead to coughing,” Thompson said.

Immunoglobulin E, or IgE, is the antibody associated with triggering an allergic response and is located on mast cells in the immune system. The pollen, combined with mold spores from damp weather, as well as environmental pollution is “the perfect storm” if you have allergies, he said.

While no one is sure why humans developed allergies, Thompson said one common theory is that it began centuries ago as a defense mechanism to get parasites off our bodies.

“It’s gone awry now … because [the immune system] reacts to things it shouldn’t,” he said.

Changes in pressure can cause sinus problems, which can be confused with allergies; many people with colds during spring may also think they have allergies.

“If it’s late April or early May and [the person] has been fine the rest of the year, it’s plausible to think it’s allergic, but it could just be a viral process also,” Thompson said.

What differentiates an allergy from sinus problems or a cold is itchiness, said Dr. Joel Klein, a board-certified allergist in the north suburbs of Chicago.

“Itching distinguishes very reliably between an allergic process and an infectious process,” Klein said.

If seasonal allergies are a common occurrence for an individual, Klein recommended beginning medication about a month prior to when allergies usually begin to act up.  This allows time to build up resistance.

“Act preemptively instead of once the symptoms start,” he said.

According to Klein, there is no difference between indoor and outdoor allergy medications, regardless of the labeling as such. Antihistamines  work whether someone is inside or out, he said.

“[Antihistamines] block molecules in the body, whatever the allergen is,” Klein said.

Dr. Laura Rogers, a board-certified Chicago allergist, said heredity constitutes a “very strong component” in whether someone develops allergies.

If one parent suffers from hay fever, there is a 50 percent chance the child will as well, and if both parents have hay fever it can be as high as 75 percent, according to Rogers.

She advised those who think they have allergies to get tested by an allergist to find out what their exact allergies are. While a blood test is often done by a primary care physician, it is not as sensitive as a skin test.

The test scratches the surface of the skin with proteins associated with allergens. If the individual has allergies, the antibodies will react and produce a localized reaction similar to a mosquito bite.

“It’s always a good idea to get a [skin] test,” Rogers said. “It’s just 15 minutes.”

Some allergens are already making their way into the air,  since the past Chicago winter was fairly mild. When the weather is less severe, pollen tends to

develop earlier because the warmer weather allows for an earlier growth.

“We see some on the radar now,” Rogers said.

Tree season starts late February and goes through May, Thompson explained. Cottonwood, which produces one of the more common allergens, begins to pollinate between March and April. Grass is usuallyMay-June and ragweed can be “nailed to the day,” he said — Aug.15 — for four to six weeks.