Spring and fall are peak allergy seasons in many areas, with spring trees still pumping out millions of grains of pollen each day and the summer grasses already starting to contribute their share. Sneezing, running nose, and itching – itchy eyes, itchy nose, itchy throat – wouldn't it be great to be able to prevent allergies before they even got started.

Preventing asthma and allergies is possible, according to a study in the June 2003 issue of Thorax. Children at high risk for asthma and allergies were recruited in 1990 to be part of this study. Half of them went about life as normal, and the other half had a low-allergy diet as infants – starting with breast milk (with moms on a low-allergy diet) or Nutramigen formula (no milk or soy-based formula). This group of families also undertook significant measures to avoid exposure to house dust during infancy.

Avoiding inhaled allergens, though, may be another story. Other studies have shown that babies who are exposed to dogs and cats before the first birthday, for example, are far less likely to develop allergies later. It seems to me that the nose is designed to detect changes (which is why you often no longer notice even very strong odors if you are around them long enough). It seems to me that a baby’s nose learns what is "normal" to have around them in the air during the first year or so, and then begins to consider some later arrivals as dangerous invaders – the body develops an allergic response to them.

Allergies happen when the body is tricked into thinking that harmless particles are dangerous invaders. The immune system tries to get rid of these allergens by sneezing them out, flushing them out with tears or mucus, or dislodging them with nose rubbing. It tries to prevent them from getting into the lungs by constricting the airways. These are all normal responses to toxins and viruses. They are allergies if the trigger is not really a problem.

There may have been other differences between the two groups in the study. One half certainly worked harder and paid more attention to allergy issues. We still have a lot to learn. What’s exciting about this breakthrough study is that it demonstrates that preventing allergies, asthma, and eczema is truly possible. Now we just have to learn how best to do it.

Ideally, each cold symptom should be treated with a single drug. However, most remedies contain a variety of drugs—antihistamines, decongestants, analgesics, expectorants (drugs that make phlegm easier to cough up), and cough suppressants—and are designed to treat a wide range of symptoms. If a congested nose is the problem, neither a cough suppressant, an expectorant, nor an analgesic is needed. If a cough is the problem, neither an antihistamine nor a decongestant is needed. If a sore throat is the only symptom, an analgesic (such as acetaminophen, aspirin, ibuprofen, or naproxen) is likely to work. Throat lozenges, especially those with a local anesthetic such as dyclonine or benzocaine, or a saltwater gargle (half a teaspoon of salt in 8 ounces of warm water) may also help. Finding an appropriate treatment for each symptom can be a challenge. Reading the labels or consulting a pharmacist can help.

Occasionally, a cold or cough may be a sign of a more serious disorder. A doctor should be consulted if symptoms last more than a week, especially if chest pain occurs or a cough produces dark phlegm. Fever and pain are unlikely to accompany a common cold and may indicate influenza or a bacterial infection.

Side effects of decongestants may include nervousness, agitation, palpitations, and insomnia. Because these drugs circulate throughout the body, they constrict other blood vessels—not just those in the nose—possibly raising blood pressure. For this reason, people with high blood pressure or heart disease should take decongestants only under a doctor's supervision or not at all. People with diabetes or hyperthyroidism also require a doctor's supervision if they take decongestants.

In an attempt to avoid these side effects, people often use nasal spray formulations, which temporarily reduce swelling in nasal tissues without affecting other organ systems. However, nasal sprays work so fast and so well that many people are tempted to use them longer than the 3-day limit listed on the label. Overuse can lead to the vicious circle of rebound nasal congestion: As the spray's effect wears off, small blood vessels in the nose can expand, causing congestion and stuffiness. This feeling may be so uncomfortable that use of the nasal spray is continued. Such use may lead to drug dependency that lasts months or years. Sometimes withdrawal has to be supervised by a doctor specializing in ear, nose, and throat disorders.

Long-acting nasal sprays contain oxymetazoline or xylometazoline, which may provide relief for as long as 12 hours. Long-acting nasal sprays can be identified by reading the label. They also should be used for no more than 3 days at a time.

Other side effects of antihistamines are less common. They include blurred vision, light-headedness, headache, stomachache, noise in the ears (tinnitus), palpitations, dry mouth, difficulty with urination, constipation, and confusion. Older people are particularly susceptible to the side effects of antihistamines (see Aging and Drugs).

Older people, pregnant women, and breastfeeding women should consult a doctor before they take any drug that contains an antihistamine. This precaution also applies to people with angle-closure (narrow-angle) glaucoma, heart disease (such as angina and abnormal heart rhythms), constipation, or an enlarged prostate gland. Despite widespread concern about these risks, most cold remedies contain antihistamines. Reading labels or consulting a pharmacist can help people identify cold remedies containing antihistamines.

Cold remedies containing antihistamines should not be taken with alcohol, sleep aids, tranquilizers, or other drugs that also cause drowsiness and decrease alertness. Such a combination may intensify the sedating effects of the drugs.

An unproductive, or dry, cough can be very irritating, especially at night. A cough suppressant can provide relief and contribute to restful sleep. Dextromethorphan, a very effective cough suppressant, is the most common ingredient in OTC cough remedies. It is not an opioid (narcotic), and it rarely causes side effects, although an upset stomach or drowsiness can occur.

Codeine, also a very effective cough suppressant, is available only by prescription in many states. However, other states permit pharmacists to sell cough remedies containing codeine without a prescription if the customer signs for it. Because codeine is an opioid, some people fear it may be addicting. In reality, addiction is uncommon. Codeine can be helpful at bedtime because of its slight sedative effect.

Codeine causes nausea, vomiting, and constipation in some people. Because codeine may also produce light-headedness, drowsiness, or dizziness, cough remedies containing codeine should not be taken by anyone who is about to drive a vehicle or perform a task that requires concentration. Allergy to codeine is uncommon. Side effects may be more likely and more pronounced when other drugs that also reduce concentration (such as alcohol, sedatives, sleep aids, antidepressants, and certain antihistamines) are taken at the same time as codeine. Consequently, such a combination should not be taken except under a doctor's supervision.

To choose a cough remedy suitable for their symptoms, people should check the list of active ingredients on the package and talk with their pharmacist. They may need a product to help them cough up phlegm (a product containing guaifenesin), to suppress the cough (a product containing codeine or dextromethorphan), or to do both. A remedy containing codeine may be useful when a cough interferes with sleep, although codine may be addictive.