Norman Klein, M.D., FAAAAI
In the case of a cold, infection or flu, the foreign bodies are harmful bacteria or viruses. The immune system attacks these invaders, which have the potential to harm the body.
In the case of allergies, the body mistakes a harmless substance, such as pollen or dust, for a dangerous invader. It then launches an attack that leads to the symptoms commonly associated with allergies.
Because these processes are so similar, the symptoms people experience with allergies often mimic those of a cold or infection. These include sneezing, nasal congestion and watery eyes.
Cold and flu symptoms generally resolve in a few days, once the body has successfully fought and conquered the invading organism. Allergy symptoms, however, may continue for as long as the person is in contact with that substance.
In rare cases, allergies can cause a severe allergic reaction (anaphylactic shock) that may result in hospitalization or even death. Therefore, it is important for people to consult a physician to determine the specific allergy triggers to which they are sensitive. Avoiding these triggers is the best defense for people with allergies.
About colds vs. allergies
Colds, infections, flu and allergies can have very similar symptoms. Therefore, it may be difficult for patients to determine which they are experiencing. In fact, allergies may be identified for the first time when a patient consults a physician about a lengthy cold.
Of course, people with known allergies are often aware they are having an allergic reaction. And not all allergy symptoms mimic those of an infection. However, there are other conditions that could cause nearly all allergy symptoms. Ruling these conditions out may be a part of any allergy diagnosis.
There are a number of infectious conditions with symptoms similar to allergies, including:
- Common cold. A virus that can be contagious to others. Patients may avoid infecting others by frequently washing their hands and avoiding contact, particularly sneezing or coughing around other people. Colds tend to occur in the fall and winter while allergies can occur at any time of the year, depending on the allergy trigger.
- Flu (influenza). A contagious respiratory illness caused by influenza viruses. Flu symptoms are similar to cold and allergy symptoms. Flu vaccine may help develop the antibodies necessary to prevent infection by a specific influenza virus. Flu is also treated with rest, time and good nutrition.
- Sinus infections. An infection typically caused by bacteria that may also be caused by a viruses or fungi. Sinus infections involve blockage and inflammation of the sinuses and can be mistaken for allergies. Unlike allergies, sinus infections may be treated with antibiotics.
- Strep throat. A contagious bacterial infection of the throat spread through direct contact with mucus from an infected person. Strep throat may be treated by a physician with antibiotics.
A good guideline for distinguishing between a cold and an allergy is time. Colds get better over time, generally in 7 to 10 days, while allergic reactions can last for months. Eating nutritious foods, getting adequate rest, and drinking plenty of water will help to alleviate cold and flu symptoms.
While colds are usually just inconvenient, allergies can be serious conditions. Some forms can lead to chronic respiratory diseases, such as asthma or chronic obstructive pulmonary disease (COPD). Other allergies can produce a potentially life-threatening reaction called anaphylactic shock that involves difficulty breathing and a drop in blood pressure.
Although allergies themselves do not involve infection, they can lead to infections. For instance, symptoms caused by allergic rhinitis, if untreated, can cause fluid to build up in the ear, leading to recurring ear infections (otitis media).
Patient education and adequate management of the allergy through consultation with a physician can control allergic diseases. A physician can diagnose the specific trigger of the allergy and provide information to avoid the trigger and/or medication to treat a reaction. Although there is no cure for allergies, there are many treatment options including allergy medications and allergy shots. Patients should consult a physician to determine the appropriate treatment options.
Related conditions for colds and allergies
There are a number of conditions that may be caused by colds or allergies. These include:
- Sinusitis. An inflammation of the sinuses that may affect the nose, eyes and ears. Sinusitis may be caused by infection, irritation or allergic reactions. Inflammation and swelling of nasal tissue caused by an allergic reaction is called allergic sinusitis. Sinusitis can be chronic (long term) or acute (short term and intense). Chronic sinusitis is the most common chronic illness in the United States. A variety of factors contribute to the development of sinusitis including colds, allergies, congenital disease, trauma, and inflammatory disease. Nasal allergies are different from sinusitis.
- Rhinitis. Rhinitis is an inflammation of the mucous membranes of the nose. Allergic rhinitis is caused by allergies and is characterized by a runny nose, sneezing, congestion, and itchy eyes, nose, throat and inner ears. Allergic rhinitis may cause sinus disease, as well as recurring ear infections (otitis media). Non-allergic rhinitis is characterized by a swollen and inflamed nasal lining, clear nasal discharge and a stuffy nose.
- Rhinosinusitis. Rhinosinusitis is an inflammatory condition that involves both the lining of the nose (rhinitis) and the sinuses (sinusitis). Nasal polyps are often associated with rhinosinusitis. Rhinitis typically precedes sinusitis, and sinusitis without rhinitis is rare. Therefore, the term rhinosinusitis is starting to replace sinusitis. Nasal allergies can produce rhinitis and symptoms that resemble sinusitis
- Conjunctivitis. Conjunctivitis is an inflammation of the eyes. It is characterized by itchy and watery eyes. The thin membranes covering the exposed surface of the eyes (conjunctiva) are active immune system tissues. Conjunctivitis may be caused by allergies, infections or irritation. The infectious form of conjunctivitis is also known as pink eye. Allergic conjunctivitis is the most common form of allergic eye disease.
- Bronchitis. Bronchitis is an inflammation of the lining of the bronchial tubes that connect the windpipe (trachea) to the lungs. When the bronchi are inflamed, less air is able to flow to and from the lungs and heavy mucus is coughed up. acute bronchitis is often associated with a severe cold. Allergic bronchitis is caused by an allergic reaction. Chronic bronchitis is associated with cigarette smoking and other environmental irritants.
- Ear infection (otitis media). An ear infection is an inflammation and/or infection of the middle ear typically proceeded by or associated with a viral upper respiratory tract infection. In many cases, allergic conditions contribute to recurring bouts of ear infection. The condition is characterized by ear pressure and pain, ear itchiness and drainage from the ear. Nausea, vomiting and fever may also occur.
Potential causes for colds and allergies
There are significant differences in the causes of allergies and infectious conditions, such as the common cold. However, both begin with a similar immune system reaction. The immune system produces antibodies to neutralize, metabolize or eliminate a substance the body identifies as foreign.
In the case of a cold, infection or flu, the foreign bodies are harmful bacteria, fungi, viruses or parasites. The immune system’s response to these invaders helps the body to lessen or prevent damage from these harmful substances. For instance, during a cold, nasal discharge can last up to two weeks. Drainage of this type is a normal part of the body’s response to viral upper respiratory infection.
In the case of allergies, the immune system launches a similar attack against a harmless substance, such as pollen or dust. Because the body processes are so similar, the symptoms people experience with allergies often mimic those of a cold or infection. These include sneezing, congestion, watery eyes and fatigue.
Allergic reactions are caused when a person comes into contact with an allergy to which they are sensitive. The most common allergens include:
- Pollen. Given off seasonally by trees, grass and weeds, pollen is responsible for triggering most cases of allergic rhinitis (hay fever). The plant most commonly associated with pollen allergies is ragweed.
- Dust mites. Many people with dust allergies are actually allergic to dust mites – microscopic insects that live in dust. Like most airborne allergens, dust mites often trigger allergic rhinitis symptoms in sensitive people. People allergic to pollen, mold or animal dander (shed dead skin) may also experience symptoms when exposed to dust.
- Foods. Almost any food may cause an allergic reaction. However, only eight foods cause 90 percent of allergic reactions: soy, wheat, tree nuts, peanuts, milk, eggs, fish and shellfish. These reactions can range from mild to the severe and life-threatening anaphylactic shock.
- Animals. People with animal allergies have sensitive immune systems that react to harmless proteins in animal dander, saliva or urine. Allergies to furred or feathered animals are common especially among people with other allergies or asthma. From 15 to 30 percent of people with allergies have allergic reactions to cats or dogs, according to the Asthma and Allergy Foundation of America.
- Mold. Allergic reactions to mold can occur during all seasons. The spores are spread by both air and wind under both dry and humid conditions depending on the mold type. It is common for people to have mold allergy if they or another family member are allergic to pollen or animal dander.
- Latex. Allergies to latex products (e.g., balloons, rubber gloves, rubber balls, condoms) are caused by proteins in rubber tree sap. There are two different types of reaction to latex. The most common is a red and itchy rash (contact dermatitis) that breaks out where latex contacts skin. In some cases latex allergy may cause the intense allergic reaction anaphylaxis. Sometimes people with latex allergy also experience reactions to tropical fruits, nuts, avocado, raw potato, tomato or celery.
- Drug allergies. Allergies to medication can cause a variety of symptoms from hives to the severe breathing problems associated with anaphylactic shock. Drug allergies are different from side effects.
- Insect stings. Most insect stings are caused by bees, wasps, hornets, yellow-jackets and fire ants. These insects have venom that may act on the human circulatory system causing the blood vessels to dilate or become wider. People with allergies to insect venom may experience anaphylactic shock following a sting.
Allergies can affect anyone regardless of age, gender, race or socioeconomic factors. There is a link between heredity and the development of allergic disease. If both parents have allergies, their biological child has a 75 percent chance of developing allergies, according to the Asthma and Allergy Foundation of America. If one parent has allergies, the child’s chance of allergy development is 50 percent. However, parents and children do not necessarily share the same allergies.
It was once thought that people would, or could, outgrow allergies. Although allergies may seem to spontaneously improve, in reality, it is believed that they become dormant and have the potential to return at a later time. There is a tendency for allergies to become less severe after age 40 and become more severe after age 60.
Other factors that may produce allergy symptoms are environmental irritants (e.g., smoke, perfume), hormones and stress.
Signs and symptoms of colds and allergies
Allergies, colds, infections and flu can be hard to distinguish as the symptoms may be similar or even identical. Common symptoms for all of these conditions include:
- Nasal congestion
Cold symptoms often start gradually and increase over a short period of time. A cold will last from a few days to a couple weeks.
Colds are also characterized by:
- Fever (usually low)
- Nasal discharge that may be yellow or green
- Sore throat
- Muscle aches
Cold symptoms that recur often, or last longer than two weeks may be an indication of an allergy. Allergy symptoms may also include:
- Skin rashes (e.g., hives, eczema)
- Clear nasal discharge
- Sneezing repeatedly
- Watery, itchy eyes
- Dark circles under the eyes (allergic shiners)
- Breathing difficulty, such as wheezing
Allergy symptoms begin almost immediately after exposure and last for as long as the person is exposed to the allergen. Left untreated, allergies may cause more serious conditions, like sinusitis. In addition, severe systemic allergies (anaphylactic shock) can be fatal. Therefore, it is important for people who suspect an allergy to consult a physician.
Diagnosis methods for colds and allergies
Regardless of whether a cold or allergy is suspected, physicians will usually begin with the patient’s medical history and a physical examination. If a cold or flu is suspected, the physician may recommend rest and a follow-up later if symptoms persist.
If sinusitis is suspected, physicians may recommend a sinus x-ray or CAT scan to produce an image of the sinus cavities. A swab of throat tissue (culture) may be taken for testing if strep throat is suspected.
Allergy testing is more involved and may include one or more of the following tests to identify the specific allergen(s) involved.
- Skin tests. These tests are the most commonly performed allergy tests and are the least time consuming and expensive. Small amounts of the suspected allergen are introduced to the skin by scratching, pricking or puncturing the skin with a needle. A raised, red itchy bump on the area of the skin where an allergen was introduced indicates an allergy to that substance. Also, the greater the skin reaction, the more sensitive the patient is to that allergen. Skin tests are considered to be about 90 percent accurate.
- Blood tests. Blood tests use radioactive or enzyme markers to detect levels of IgE antibodies. These tests are useful if a widespread skin rash makes skin testing difficult, or if the patient has the potential for a sudden and severe allergic response to the test allergen(s). Blood tests are considered to be about 90 percent accurate.
- Elimination diets. An elimination diet is used to help isolate sensitivity to specific foods. The eight foods that most frequently cause allergies (soy, wheat, tree nuts, peanuts, milk, eggs, fish and shellfish) are not included in the initial diet. The patient stays on the prescribed diet for four to seven days. If the symptoms continue, additional foods are removed from the diet until the symptoms stop. Once the symptoms disappear, new foods are added to the basic diet, one at a time, until the symptoms reappear. The key to the success of the elimination diet is consuming pure foods. Many processed foods contain small amounts of common allergens, which can affect the accuracy of the elimination diet for diagnosing food allergies.
Treatment options for colds and allergies
Allergies, colds and infections have similar symptoms and treatments focused on relieving these symptoms are often the same. Medications that may be used to treat both allergies and colds include:
- Antihistamines. Medications used to treat symptoms such as sneezing, runny nose and itchy and watery eyes. For allergies, antihistamines can be taken either after symptoms begin or on a regular basis, to prevent symptoms from occurring.
- Decongestants. Medications used to reduce nasal congestion, swelling and redness. They work by constricting swollen nasal tissues, which prevents fluid and mucus from forming.
- Nasal sprays. Medications, used to reduce nasal allergy and cold symptoms, that are delivered as a fine mist directly into the nasal passages. A variety of medication can be delivered in this manner, including antihistamines, corticosteroids, decongestants and lubricating medicines.
- Eye drops. Medications dropped directly into the eye to relieve eye-related symptoms. A variety of medication can be delivered in this manner, including antihistamines, decongestants and sterile solutions to lubricate eye tissue.
For colds, infections and flu-like symptoms, adequate rest, a nutritious diet and time are often the best treatments. With the exception of diet, these factors will have little effect on allergy sufferers. Medications that may be used to treat cold-like symptoms, but not allergies, include:
- Expectorants (medications which help thin mucus)
- Cough suppressants
- Aspirin and other pain relievers or fever reducers
- Antibiotics (for bacterial infections only)
For allergy sufferers, all treatments will involve avoiding the allergen that triggers a reaction as much as possible. Once the source of the allergy is diagnosed, a physician can determine the most appropriate treatment methods for each patient. Allergy treatment may also include medications to:
- Reduce inflammation (e.g., NSAIDs or corticosteroids)
- Open breathing passages and reduce mucus in lungs (e.g., bronchodilators, anticholinergics)
- Reverse life-threatening symptoms of anaphylaxis (e.g., epinephrine)
- Prevent the onset of allergy symptoms (e.g., antihistamines, leukotriene modifiers, corticosteroids, mast cell stabilizers, anti-IgE antibodies)
Allergy shots (immunotherapy) are another potential allergy treatment. Aimed at reducing symptoms or the frequency of allergic reactions, the treatment involves injecting the patient with gradually increasing amounts of a specific allergen over a period of time. The method is not always effective and not appropriate for all patients.
Prevention methods for colds and allergies
For both colds and allergies, prevention centers on lessening the risk of exposure to the allergens, viruses or bacteria that lead to symptoms. In the case of colds, this involves keeping the immune system at peak performance by maintaining a rested, exercised and well-nourished body. The risk of introducing bacteria or viruses into the body can also be reduced by washing hands frequently. However, not all colds and infections can be prevented.
Prevention of allergic reactions can be more complex, depending on the type of allergens to which a person is sensitive. It is not completely understood why some people develop allergies and other do not. Therefore, it is not currently known how a person can prevent developing an allergic condition. There is some evidence to suggest that breastfeeding helps prevent children from developing food allergies and eczema. However, this link is not yet proven.
Prevention strategies for people with allergies focus on reducing the frequency or severity of allergic reactions. Total avoidance of any known allergens is the only treatment that can completely prevent an allergic reaction from occurring. However, avoiding an allergen is often difficult when the allergen is constantly present or an individual is highly sensitive.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about colds vs. allergies:
- How can I tell the difference between a cold and an allergy?
- Do my symptoms suggest an allergy?
- Are there tests that can be use to diagnose my cold or allergy?
- Are there medications available to treat my symptoms? If so, how effective are they?
- Can I use cold medicine to treat my allergy symptoms and vice-versa?
- When can I expect my symptoms to subside?
- What steps can I take to prevent colds and allergy symptoms?
- Are there steps I can take to prevent an allergy from developing in the first place?