So you've had a runny nose, sneezing, head congestion and ear fullness. It's another cold, right? But this "cold" seems to be lasting forever. Over-the-counter cold medicines have helped a bit, but they also make you drowsy.

This is the stage when most people will throw in the towel and finally seek medical attention. With the symptoms lingering, your health care provider can help you determine whether you have a cold or allergies.

The first clue to the possibility of allergies is the prolonged nature of the illness. Colds don't last forever. Cold viruses cause your immune system to respond within a couple of weeks to cure the cold. That isn't true with allergies.

With allergies, a person has continual exposure to something called an allergen. An allergic response actually causes your immune system to work against you, although it causes symptoms similar to a cold -- runny nose, sneezing, head congestion and ear discomfort.

Allergens also can cause itchy nose, eyes, ears and the roof of your mouth, pressure in your sinuses and dark circles under your eyes (which you may initially attribute to a lack of sleep). You may develop hives or a dry, scaly rash, both of which are itchy.

If there is enough of a trigger or exposure to the allergen, it can cause you to wheeze and feel short of breath, leading to asthma. If untreated, allergies can lead to missed school and work days, and possibly to a trip to the emergency department.

There are many allergens -- given enough exposure -- that can lead to allergies. Your health care provider will help to determine the possible cause of your allergic reaction.

It may depend on the time of year your symptoms typically occur. For example, symptoms during the spring may indicate tree-pollen allergies. Grass pollens are prevalent during the summer, and ragweed can cause problems in the fall.

There are also allergens that cause symptoms in the winter when you are indoors. Exposure to common household "residents" such as molds and dust mites can lead to allergies. Pets -- more specifically, their dandruff and saliva -- may also cause symptoms.

Other allergens, including drugs, foods and insect stings, can cause very serious reactions such as airway difficulties and shock, in addition to the symptoms already mentioned. In these cases, avoiding exposure to the known allergen and/or carrying a special self-injection pen of medicine can save a person's life.

To alleviate the symptoms if you have allergies, you can take antihistamines that counteract the chemical your body releases when you come in contact with the allergen. Antihistamines can be obtained over the counter or by prescription.

A steroid nasal spray can help with nasal congestion, and eye drops can help with itchiness of the eyes. Your clinician will help you determine what is best for you.

If medication does not give you relief, you may be referred to an allergist, a physician who specializes in testing and treating allergic disorders.

Skin testing or blood tests may be done to specifically determine what you are allergic to.

Another solution is immunotherapy, which involves injections on a regular basis for six months to several years. In immunotherapy your body is given a small dose of what you are allergic to so that your immune system develops protective antibodies to lessen or eliminate your symptoms -- like taking multiple vaccines for your allergies.

For a "Do You Have a Cold?" self-assessment checklist, see http://www.sa.psu.edu/uhs/ healthinformation/selfassess/cold.cfm.