Sneezing. Itchy, watery eyes. Nasal congestion. Sinus pressure.

It may sound like the worst cold ever, but if you are one of the millions of Americans living with allergies, you know these symptoms can last for weeks, months or even year-round.

Sure, there are simple tasks a person can do to lessen their allergic symptoms. For example, washing your hair before you go to bed to rinse the allergens out of it may be helpful. Severe allergy sufferers are sure to keep their house super-clean, not a speck of dust in sight.

However, the only real way to prevent or stop an allergy attack, is by taking medicine, Dr. Cascya Charlot of The Allergy and Asthma Care of Brooklyn, N.Y., told FOXNews.com.

But with all the medicines advertised on television and in magazines, how do you know which one does what?

Charlot broke it down for us:

1. Antihistamines

This class of drugs is broken down into two groups: a first-generation and a second-generation.

The first-generation of drugs are histamine-receptor blockers, and can usually be bought over-the-counter (for example, Benadryl).

Histamine receptors are located all over the body — on your skin, in your nose, in the airways — basically anywhere you can have allergic symptoms, Charlot said.

So when different allergens bind themselves to the mast cells, they release histamines, thus creating the symptoms of allergies (runny nose, itchy, watery eyes).

The downside of taking an antihistamine is that it tends to make you drowsy, Charlot said, since it goes through the blood-brain barrier.

The upside is that they are cheaper than most other medications.

The second-generation of antihistamines do not cross the blood-brain barrier, which is why they tend to cause less drowsiness, but they still block histamine receptors. Examples of these medications are Claritin, Zyrtec (over-the-counter) and Allegra, which needs a prescription.

2. Decongestants

Decongestants usually contain pseudoephedrine and they do not block histamine receptors, but they do relieve nasal and sinus congestion or pressure, Charlot said.

A popular decongestant is Sudafed, which is available behind-the-counter, but without a prescription, because of concerns that it can be used to manufacture methamphetamine.

Another kind of decongestant is phenylephrine, which is available in many over-the-counter products like Tylenol Sinus. Unlike pseudophedrine, this drug is sold on store shelves rather than behind the counter.

These decongestants work by shrinking the blood vessels in the nose or sinuses.

Charlot said she prefers not to recommend pseudoephedrine products because of their side effects: increase in blood pressure, heart rate, heart palpitations and nervousness.

Sometimes an antihistamine like Allegra will contain pseudoephedrine, in which case it would be labeled "Allegra-D."

3. Leukotriene Receptor Blockers

This is a new class of allergy medication, Charlot said.

In fact, it’s so new there is only one medication in the class, and that’s Singulair, which was FDA-approved to treat asthma many years ago, but was FDA-approved to treat seasonal allergies in 2003 and year-round allergies in 2005, Charlot said.

“(The drug) blocks leukotrienes, an important contributor to allergy symptoms," Charlot said.

Charlot said she usually prescribes this medication in addition to an antihistamine.

4. Intra-Nasal Steroids

Nasal steroids are anti-inflammatory medications that block the production of cells in the immune system that cause allergic symptoms, Charlot said, but you’ll need a prescription from your doctor in order to obtain one.

Examples of nasal steroids include Flonase, Nasonex or Veramyst.

These sprays "inhibit the production and release of inflammatory secretions such as leukotrienes, histamines, tryptase and interleukins, thus decreasing inflammation," Charlot said.

You may be inclined to use a decongestant nasal spray because of its quick relief — the kind you can buy over-the-counter, but be aware that those can only be used for three days because of the risk of rebound congestion.