Allergies are an unfortunate part of life that many people learn to suffer through. Whether it’s seasonal grass or ragweed, ever-persistent indoor dust mite issues, or dreaded side effects from a visit to a dog or cat lover’s home, chronic allergies negatively affect the lives of up to 30% of adults in the US (1).
What causes allergies?
When the immune system reacts to a substance and recognizes it as foreign, it will produce many white blood cells to attack this foreign antigen. White blood cells release chemicals as a part of their attacking response, the most common being histamine. These chemicals dilate blood vessels, producing symptoms like a runny nose, sneezing, and itching, watery eyes (2). This immune response is known as allergic rhinitis, or hay fever. Rhinitis can be either seasonal or perennial, depending on when symptoms seem to spike. Those with seasonal allergic rhinitis find themselves reacting most strongly in spring, summer, and fall against the higher levels of airborne mold spores or tree, grass, or weed pollen. Perennial allergic rhinitis, on the other hand, usually occurs in reaction to year-round indoor antigens, such as dust mites, cockroaches, certain types of mold, and pet hair or dander (3).
Treatments for Allergies
The most common treatments for rhinitis largely involve managing symptoms. We’ve all heard of antihistamines, which are available over-the-counter and work to directly mitigate the effects of the immune response of histamines discussed above. Intranasal corticosteroids, nasal sprays, decongestants, and other drugs all work to reduce symptoms, as well. Other suggestions for managing rhinitis involve taking measures to simply avoid allergens, such as keeping windows shut during high-pollen seasons, avoiding contact with animals or homes that have animals, or investing in dust mite-proof mattress covers (3).
Unfortunately, none of these treatments create long-term tolerance for the allergens, so they must be used each time an allergen presents itself and symptoms arise. While taking medication to curb symptoms every day may be sufficient for some, for those that find the treatment listed above aren’t sufficient, do not like the side effects of allergy medications, or are seeking long-term relief, there is an alternative option that many have turned to, allergy immunotherapy.
Immunotherapy is the process of exposing the immune system to increasingly large amounts of allergens, resulting in increased tolerance to the allergens and a decrease in rhinitis symptoms over time. In other words, white blood cells build up a tolerance, so it begins to take a lot more of the allergen to get them to produce the same levels of the symptom-producing chemicals mentioned above (4). It is unique in that it is the only type of treatment that can cause long-term improvement of symptoms, even after treatment ends (5, 12). In the United States, subcutaneous (under the skin) immunotherapy has been the standard for allergy therapy, which involves receiving shots from a healthcare professional two or more times a week. However, sublingual (under the tongue) immunotherapy is seeing a rise in popularity, which can deliver the same results but through safer, far more convenient means (9).
Subcutaneous vs Sublingual Immunotherapy
Both types of immunotherapy begin by talking to an allergist about your health history, as well as completing either a skin- or blood-based allergy test (6). These will determine the severity and types of your allergies. Based on your results, your allergist will prescribe specific doses of allergens within your allergy shots or allergy drops/tablets.
Both types of immunotherapy have three stages of treatment, and both require anywhere from 2-5 years to provide long-term results (5). The first stage involves creating an initial tolerance. The immune system will slowly adjust to receiving the treatment, and any overt reactions to the immunotherapy, like itching at the site of treatment, will diminish during this time. Some patients even find that their general allergy symptoms may begin to decrease as well (12). This usually takes about 1-3 months.
The second stage takes more time, anywhere from 3 months to 2 years. Allergen tolerance in the body is actively increasing during this time, and most people find that their symptoms are greatly decreased, if not eliminated fully (7).
Stage three can be considered the most crucial stage for long-term results. By continuing allergen exposure to the body even after symptoms become more manageable, the immune system builds more and more tolerance, which allows for long-term symptom relief even after you stop immunotherapy. This last stage may take up to two years (5).
Subcutaneous immunotherapy (SCIT) involves receiving shots from your doctor on a schedule ranging from daily to weekly, with the frequency of shots decreasing over time (5). Sublingual immunotherapy (SLIT) comes in the form of drops or tablets, each with a controlled dose of allergens. The medicine is placed under the tongue for 20 seconds to 2 minutes each day and is quickly absorbed by the cells underneath your tongue (8). While allergy shots (SCIT) are quite effective, there are a number of advantages to choosing allergy drops or tablets (SLIT).
Greater Safety Profile
Sublingual immunotherapy has a greater safety profile than subcutaneous immunotherapy, with fewer systemic reactions overall, and no fatal anaphylaxis cases reported (10). Additionally, for those who have not been able to tolerate SCIT due to adverse reactions, SLIT is usually still an available alternative (10). Beyond that, evidence of severe asthma attacks that occur as a result of sublingual immunotherapy aren’t due to allergen dose, whereas asthma attacks due to subcutaneous treatment are directly related to an increased dose level (6). In multiple studies, SLIT resulted in fewer severe reactions than SCIT did, including fewer severe asthma attacks and anaphylaxis (11).
Aside from the manner of administration, the safety of SLIT also lends to its convenience. The risk of severe allergic reactions is so low that only the first dose needs to be taken at your doctor’s office. After that, the rest of the doses are safe to be administered on your own at home.
More Convenient and Accessible
Beyond its safety, SLIT’s largest selling point is its convenience. While SCIT can require twice-weekly visits to your doctor’s office, immunotherapy drops or tablets can be administered on your own each day. As mentioned above, the process involves putting the drops or tablets under the tongue and letting them dissolve for 20 seconds to 2 minutes. This eliminates the required time spent at the doctor’s office to receive allergy shots, which opens up immunotherapy treatment to many who would not have been previously able to commit to it. For those who travel often, live rurally, don’t have the flexibility to take time off work, or find it hard to get to their doctor, being able to administer this medicine themselves can be a huge deciding factor in whether they can commit to allergy immunotherapy. The convenience of drops can also be a deciding factor or those who have a hard time tolerating needles.