Allergic rhinitis, also known as hay fever, affects approximately 20 percent of people of all ages. The most common symptoms include nasal itching, watery nasal discharge, sneezing, itchy red eyes, sore throat, or hoarse voice. Allergic rhinitis is caused by a nasal reaction to small airborne particles called allergens (substances that cause an allergic reaction). In some people, these particles also cause reactions in the lungs (asthma) and eyes (allergic conjunctivitis).
One of the first steps in treating any allergic condition is to avoid or minimize exposure to the allergens that cause the condition. Although this is frequently helpful in reducing symptoms, there may be a trade-off between avoidance and quality of life. Where avoidance is inadequate to control symptoms, clinicians have many tools to treat allergies. Allergen avoidance should never be so severe as to isolate individuals from social interactions.
IDENTIFYING THE ALLERGEN
There are four major categories of allergens that trigger allergic rhinitis:
- Pollens (spring and summer – trees, grass; fall – ragweed, tumbleweed)
- Insects (house dust mites, cockroaches, ladybugs)
- Animal allergens (skin, fur, feathers, saliva)
In some cases, it is easy to identify a person’s triggers, based upon when symptoms develop (eg, during a particular season, after exposure to a dog or cat, etc). In people with year-round symptoms, it may be more difficult to pinpoint the allergen(s).
The first step in the treatment of allergic rhinitis is to reduce exposure to allergens. The most common indoor allergens are dust mites and cat and dog dander . However, with indoor allergens, it may take three to six months to see an improvement in symptoms once triggers are removed. Steps to reduce allergens are discussed later in this topic review. (See ‘Reduce exposure to triggers’ below.)
First-line treatment also usually includes one or more medications (eg, nasal glucocorticoid sprays, antihistamines). Medications for allergic rhinitis and allergic conjunctivitis are discussed in separate topic reviews. (See “Patient education: Allergic rhinitis (Beyond the Basics)” and “Patient education: Conjunctivitis (pink eye) (Beyond the Basics)”.)
If symptoms are severe or persist despite avoidance of the allergen, the person may be referred to an allergy specialist for further testing and treatment. Allergy specialists can identify each person’s triggers, so that he or she can focus on reducing exposure to the triggers that are important for him or her.
REDUCE EXPOSURE TO TRIGGERS
Once a person’s trigger(s) have been identified, the next step is to reduce exposure to those specific allergens. Triggers may be present at work or at home, although for most people, the home environment is the primary source. It is especially important to reduce exposure to triggers in the bedroom because most people spend a significant number of hours there. However, to be effective, changes must be made throughout the entire home
Dust mites — Dust mites are a microscopic type of insect that live in bedding, sofas, carpets, or any woven material. Dust mites do not bite and do not cause harm to humans, other than by triggering allergies.
Mites absorb humidity from the atmosphere (ie, they do not drink) and feed on organic matter (including shed human and animal skin). They require sufficient humidity and nests to live in (which are not visible with the naked eye). Dust mite infestation is less common in dry climates, such as the southwestern United States.
Exposure to dust mites can be reduced by encasing pillows, mattresses, box springs, comforters, and furniture in mite-impermeable barriers. When covering crib mattresses and children’s mattresses and pillows, only tight-fitting, commercial covers intended for this purpose should be used. Homemade covers (for example, plastic sheeting fastened with duct tape) should not be used in children’s beds, as these can come apart, and children can become trapped or suffocate. Tightly-woven fabrics with a pore size of 6 microns or less are very effective at controlling the passage of mite as well as cat allergens. Fabrics with a pore size greater than 2 microns still permit airflow [3,4].
Mites can be eliminated by washing sheets and blankets weekly in warm water with detergent or by drying them in an electric dryer on the hot setting (table 2). Exposure can be further reduced by vacuuming with a vacuum cleaner equipped with a high-efficiency particulate air (HEPA) filter, dusting regularly, and not sleeping on upholstered furniture (eg, couches). However, studies have yet to show that physical or chemical cleaning methods reduce mite levels to a degree that improves symptoms .
Indoor humidity levels should be kept below 50 percent. Inexpensive humidity monitors can be purchased at most hardware stores. Humidifiers make the problem worse and are not recommended.
When possible, the amount of clutter, carpet, upholstered furniture, and drapes should be minimized, and horizontal blinds should be eliminated in the rooms where the person spends the most time (bedroom, study, television room). Washable vinyl, roller-type shades are optimal. For children, the number of stuffed toys in the bedroom should be minimized.
Animal dander — Animal dander is made up of the dead skin cells or scales (like dandruff) that are constantly shed by animals. Any breed of dog or cat is capable of being allergenic, although the levels given off by individual animals may vary to some degree. In cats, the protein that causes most people’s allergies is found in the cat’s saliva, skin glands, and urinary/reproductive tract. Accordingly, short-haired cats are not necessarily less allergenic than long-haired animals, and furless cats have allergen levels similar to furred cats.
Other animals, such as rodents, birds, and ferrets, can also trigger symptoms in an allergic individual. Pets without feathers or fur, such as reptiles, turtles, and fish, rarely cause allergy, although deposits of fish food that build up under the covers of fish tanks are an excellent source of food for dust mite colonies.
If a person is found to be allergic to a pet, the most effective option is to remove the pet from the home. Limiting an animal to a certain area in the house is not effective, because allergens are carried on clothing or spread in the air. Once a pet has left a home, careful cleaning (or removal) of carpets, sofas, curtains, and bedding must follow. This is particularly true for cat allergens because they are “sticky” and adhere to a variety of indoor surfaces. Even after a cat has been removed from a home and it has been thoroughly cleaned, it can take months for the level of cat allergen to drop. For this reason, it may take months for the person’s symptoms to fully reflect the absence of the pet.
If it is not possible to remove the animal, measures can be taken to decrease exposure to the animal dander (table 3), although none of these methods are as effective as removing the animal. Vacuum cleaners with a HEPA filter are effective in reducing cat and dog allergen levels in the home and can reduce symptoms . (See ‘Air filters’ below.)
Rodents — Mice and rats have proteins in their urine that can cause allergies. This applies to rodents that live in a laboratory setting, as well as rodents that live in the wild.
To reduce rodent allergen levels significantly, a combination of pest control methods, in addition to pesticides (eg, poison baits), are usually necessary. This includes keeping food and trash in covered containers, cleaning food scraps from the floor and countertops, and sealing cracks in the walls, doors, and floors.
Cockroaches — Cockroach droppings contain allergens that can trigger asthma and allergic rhinitis in sensitive individuals. Cockroaches thrive in warm, moist environments with easily accessible food and water. Unfortunately, efforts to control cockroach populations in infested areas are often less than successful. Still, certain measures are recommended:
- Use multiple baited traps or poisons
- Remove garbage and food waste promptly from the home
- Wash dishes and cooking utensils immediately after use
- Remove cockroach debris quickly
- Eliminate any standing water from leaking faucets or drains
- Keep humidity levels less than 50 percent with a dehumidifier or air conditioner
- Consult a professional exterminator for large or recurrent infestations
Asian ladybugs — Asian ladybugs were previously imported to the United States as a biologic means of controlling aphids. It was anticipated that the insects would not survive the cold of winter. However, they adapted by moving inside houses when temperatures drop in the early fall. Allergies to Asian ladybugs have been increasingly reported as a source of seasonal indoor respiratory symptoms, particularly chronic cough, rhinitis, and asthma. Most cases have been reported in rural areas of the central, midwestern, and southern United States. The insects can also bite and cause local reactions.
Asian ladybugs enter homes through external cracks and crevices and then infest spaces within walls. They secrete a brown liquid that may stain walls and produce an unpleasant smell.
Treating the exterior of the house with a chemical (pyrethroids) before cold weather arrives can prevent swarming of the ladybugs inside the home. Pyrethroids are similar to pyrethrins, which are derived from marigold flowers. Pyrethrins are broken down by the sun and do not significantly affect groundwater quality.
Indoor molds — Mold spores can trigger symptoms of allergic rhinitis in allergic patients. Mold thrives in damp environments. Areas, such as air conditioning vents, water traps, refrigerator drip trays, shower stalls, leaky sinks, and damp basements, are particularly vulnerable to mold growth if not cleaned regularly. Most of the mold spores enter the home from the outside air. However, under certain circumstances, mold growth in the home can be significant and worsen allergy symptoms.
To reduce the growth of mold in the home, it is necessary to remove existing mold and also to reduce humidity to prevent future growth of mold. Humidity can be reduced by removing sources of standing water and persistent dampness. Removing house plants, fixing leaky plumbing, correcting sinks and showers that do not drain completely, removing bathroom carpeting that is exposed to steam and moisture, using exhaust fans in the bathroom when bathing, and dehumidifying damp areas to levels below 50 percent are a few steps that can help to reduce or prevent growth of indoor mold.
Indoor garbage pails should be regularly disinfected, and an electric dehumidifier should be used to remove moisture from wet or humid basements. Old books, newspapers, and clothing should be discarded or donated rather than stored. Water-damaged carpets and wall or ceiling boards should be thrown out because it is difficult or impossible to eliminate mold in this situation, even with thorough cleaning.
Mold thrives on soap film that covers tiles, sinks, and grout. Sinks, tubs, and other surfaces with visible mold growth should be cleaned at least every four weeks with dilute bleach (1 ounce [30 mL] bleach diluted in 1 quart [1 liter] of water).
Air filters — Air filtering devices, including HEPA filters, other mechanical filters, and electrostatic filters, are widely advertised to reduce indoor allergens. These may be marketed as components of heating or cooling systems, as individual units for use in a room or area, or as units that are worn by individuals. These devices are expensive, and none have been scientifically proven to significantly improve allergy symptoms. Certain types of air filters (eg, ionizers) produce ozone, which is a respiratory irritant for some people. These devices have not been proven safe or effective and are not recommended.
There are several factors that interfere with how well air filters work, and these may partly explain why studies have shown mixed results:
- Air filters do not remove dust mite allergens effectively, because these allergens are relatively heavy and do not stay airborne for more than a few minutes (for example, after making a bed or disturbing a dusty cushion).
- Most air filters probably remove pollens and pet danders from the air because these allergens are light and remain airborne. However, if there is a pet, carpeting, upholstered furniture, access to outside air, or some other reservoir of allergen in the vicinity, the allergen is continuously released from these items as people move around the house. There are far more allergens in these reservoirs than an air filter can remove. Therefore, allergens continuously enter the air, even as it is being filtered, and the benefit of an air filter is minimal.
- In contrast, in a room where there are no carpets, drapes, upholstered furniture, access to outside air, and pets are not allowed, an air filter may improve air quality.
In addition, a vacuum cleaner with a HEPA filtration system and a double thickness vacuum bag can help to reduce allergen levels. This is recommended to avoid rebreathing the debris that is captured by vacuuming. A controlled trial has reported a reduction in cat and dog but not dust mite allergen levels and a clinical improvement in asthma and allergic rhinitis symptoms in homes cleaned with vacuums equipped with HEPA filters, compared with vacuums without specialized filters .
Allergic rhinitis symptoms that worsen when outdoors and at certain times of year are likely to be triggered by an allergy to pollen, other plant material, or molds.
Affected individuals should close the windows of the car and home, stay indoors when possible, and use air conditioners to filter the air during times of peak symptoms. Use of a high quality mask may be helpful for activities, such as grass cutting or wood cutting. These are also helpful in avoiding nonspecific irritants, such as dust and fumes, which can trigger sneezing. Showering before bed removes allergens from hair and skin and can help reduce contamination of the bedding. Over-the-counter saline sprays and rinses can be used after being outdoors to wash away allergens from the nasal lining.