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The common cold is a viral infection of the membranes that line the nose, sinuses, throat, and airways. Colds are one of the most common infections in humans. In fact, colds are responsible for more missed days from school and work than any other illness. A cold typically lasts about a week and clears up on its own. Occasionally, a bacterial sinus infection or ear infection will complicate a cold—especially in children. A cold can also make an existing breathing problem such as asthma worse.

Causes

Colds occur when a virus enters the body through the mucus membranes lining the nose, eyes, or throat, causing an infection. A cold virus becomes airborne when someone who has a cold sneezes or coughs. Simply breathing in infected air is one way colds are transmitted; they can also be transmitted if you shake hands with someone who has a cold, and then rub your nose or eyes. You can also get a cold from touching a doorknob or using a telephone receiver that is covered with the virus, and then touching your eyes or nose.

More than 200 different viruses can cause a cold. The most common offenders are the rhinoviruses (“rhino” means nose, the nose being a common portal for cold viruses).Coronaviruses, named after their resemblance to a crown, are responsible for about 10% to 20% of colds. The influenza and respiratory syncytial viruses cause some colds, but are more frequently implicated in lower respiratory tract infections.Contrary to popular belief, you can't catch a cold simply by being cold, underdressed, or out in the rain.

Symptoms

Colds can produce an array of symptoms, including a runny or stuffy nose, throat irritation, coughing, and sneezing. Symptoms usually appear one to three days after infection. Symptoms are typically worse in the morning, and abate as the day goes on. A sore throat or runny nose may be the first sign of a cold. Often, nasal discharge is clear and profuse in the beginning, and becomes thicker, yellowish-green in color, and less abundant as the cold progresses. Sometimes colds produce congestion and a cough. Headaches are a fairly common cold symptom, but fever is rare. The average cold lasts about seven days, and symptoms tend to be the worst on the third day. However, some symptoms—a cough especially—may persist into the second week.

Sinus infections and ear infections can complicate a cold and prolong symptoms. Ear infections accompany about 5% of colds in children. People with bronchitis, asthma, and other conditions that interfere with breathing may experience added breathing difficulty during or after a cold.

Table 1. Symptoms of the Common Cold

Sore, scratchy throat Nasal discharge—thin and clear or thick and yellowish-green Sneezing Cough Headache General malaise

Risk Factors

Colds occur most frequently during childhood. Because their immune systems are less developed, and because they tend to wash their hands less frequently than adults, children under the age of 5 get more colds than people in any other age group. Children may get as many as six to eight colds a year, whereas an adult may have just one or two annually. Colds occur least often in the elderly population. By age 60, a person might get one cold a year, if that. Once you have had a cold, you will develop immunity to the strain of virus that caused it. Therefore, getting a cold becomes less likely as you age.

The various types of cold-causing viruses peak at different times throughout the year. Rhinoviruses cause colds year-round, but are more prevalent during early fall and spring. Coronaviruses are most prevalent in late fall, winter, and early spring. The influenza and respiratory synctial viruses typically infect people in late fall and winter.

Diagnosis

A cold is diagnosed based on symptoms alone. Although it can be hard to tell the difference between a cold and Influenza A, a more serious infection, colds are diagnosed based on symptoms alone. If your illness comes on suddenly and you have a high fever, your doctor will be inclined to think that you have influenza A. He or she may order to tests to see if you have Influenza A. Some bacterial infections and allergies produce symptoms that resemble a cold as well. If your doctor is concerned about a serious sinus infection, he or she may order a CT scan of your sinuses.

Because colds are not considered to be a serious medical condition and typically clear up without treatment, your doctor won't bother to test samples of tissue or secretions unless he or she thinks you could have another type of infection.

Prevention and Screening

Wash your hands regularly, and avoid rubbing your nose and eyes. Because colds often are spread by touching infected surfaces, washing your hands frequently is your best defense. Use soap and warm water, and rinse your hands for at least 30 seconds. Avoid touching your nose, eyes, and mouth if you haven't washed your hands first.

Avoid sharing objects with anyone who has a cold. Don't drink from the same glass or use the same towel or pillow. At work, try not to touch a computer keyboard or telephone receiver that a colleague with a cold has recently used.

A substance called interferon, when delivered nasally, may prevent some rhinovirus infections. Interferon enhances the ability of the cells to resist some viral strains. However, interferon may irritate the nasal passages and cause nosebleeds. Interferon is not effective against every cold-causing virus.

Research on vaccines that guard against some of the rhinoviruses is underway. Like interferon, however, these vaccines are of questionable value because there are hundreds of viruses capable of causing colds, and no one vaccine to provide protection against all of them.

Treatment

Urgent Care

See your doctor if your cold lasts longer than 10 days or if you develop severe symptoms, such as a fever or shortness of breath. If your baby has a cold, call your baby's doctor within the first day. If your symptoms persist beyond 10 days, you may have acquired an additional infection, and should see your doctor. Signs that your cold has become complicated by another illness include a temperature above 102° F (38.9°C), shortness of breath, earache, facial pain, a persistent sore throat, and a dry, painful cough.

Table 2. Warning Signs of Complications

Temperature that rises above 102° F (38.9°C) Temperature that stays above 100° F (37.8° C) for three days Earache Persistent sore throat Facial pain Dry, painful cough that will not go away Shortness of breath or wheezing

Self Care

Stay home when you have a cold. While a cold is not a serious illness, it can be somewhat debilitating, and may inhibit your productivity at work or school. Staying home will allow you to rest and recover, and will keep you from spreading your cold to others. The common cold is contagious for about three days, starting the day before symptoms appear
Rest and drink plenty of fluids.

Drinking lots of fluids (water is best) will help keep your secretions loose, and make them easier to expel. Likewise, inhaling steam or mist from a vaporizer can help keep mucus membranes from drying out, and facilitates the expulsion of excess mucus. If you have a sore throat, try gargling with warm salt water, which can be soothing. Saline nose drops may help clear nasal passages that are clogged.

Use symptom-specific over-the-counter medications. Over-the-counter pain relievers are good for a headache and the general aches and pains of a cold. Acetaminophen and ibuprofen are preferred, as aspirin may increase viral shedding, and can cause Reye's syndrome (a potentially fatal illness) in children under 16 years of age. If you have a history of ulcers or past bleeding disorders, you should check with your doctor before taking medication containing ibuprofen.

A nasal decongestant can help loosen secretions and keep the upper respiratory tract clear, and an antihistamine can dry a runny nose and reduce sneezing. Antihistamines, however, are associated with many negative side effects, including drowsiness. Cough suppressants generally are not recommended for a cold because coughing is a good way to clear secretions. If a cough is so severe that it disturbs your sleep, however, you may want to use a cough suppressant at night.

Table 3. Self-care Checklist

Drink plenty of fluids. Water, hot tea with honey, juice, and chicken soup can help loosen mucus and other secretions Use a vaporizer to keep mucus membranes from drying out Gargle with salt water (one quarter teaspoon of salt mixed with eight ounces of water) to soothe a sore throat. The same concoction can be used for saline nose drops, which may help keep the nasal passages clear Take acetaminophen or ibuprofen for headaches and general aches and pains Use a nasal decongestant to loosen secretions if congestion is stubborn Take an antihistamine if a runny nose is bothersome If a cough is disturbing your sleep, use a cough suppressant

Drug Therapy

Your doctor is the best source of information on the drug treatment choices available to you.

Alternative Medicine

Some natural remedies may help you fight a cold. The herb echinacea has been touted as a way to prevent colds, or to help speed recovery. In one study of people who were prone to getting colds, those who used the herb for two months were 35% less likely to catch a cold than those who took a placebo. Proponents say echinacea works by stimulating the immune system to fight the cold virus. Echinacea, however, may overstimulate the immune system and worsen autoimmune problems such as rheumatoid arthritis and lupus.

Vitamin C will not prevent a cold, but may shorten its duration. One review of the available research on the link between vitamin C and colds revealed that taking very large doses (1,000 mg to 6,000 mg) daily at the onset of a cold would shorten its duration by one day. However, the RDA for this vitamin is just 60 mg. Megadosing vitamin C can cause diarrhea, and can interfere with the absorption of important minerals. Anyone with kidney stones, kidney disease, or hemochromatosis should not take large doses of vitamin C.

Zinc may protect against colds and other infections. The mineral zinc is needed for the immune system to function properly. In one study of people who were just coming down with a cold, those who took zinc lozenges recovered faster (about three days on average) than those given placebo lozenges. Large doses of zinc can induce nausea, vomiting, and diarrhea. Taking more than 100 mg of zinc daily on a long-term basis, however, can hurt the immune system and interfere with copper absorption.

Prognosis

A cold is a common but minor illness that doesn't need treatment, and rarely has complications. While colds may be somewhat of a nuisance, they usually are not serious, and clear up in about a week without treatment. Using home remedies or over-the-counter medications can ameliorate symptoms, but will not speed healing. Some natural remedies may be beneficial.