If you or your child has been diagnosed with allergies to pollen, dust mites, or other environmental triggers, you may be exploring options beyond daily medications. Sublingual immunotherapy, commonly called SLIT, offers a way to retrain the immune system using small doses of allergen placed under the tongue. Like allergy shots, SLIT works with your immune system’s natural learning capacity to create lasting change, but with the convenience of home administration.
What Is Sublingual Immunotherapy?
Sublingual immunotherapy involves placing a small amount of allergen, either as a dissolving tablet or liquid drops, under the tongue daily. The tissue under the tongue is rich in immune cells that can "sample" the allergen and begin the process of teaching the immune system to tolerate it rather than overreact.
This approach has been used successfully in Europe for decades. It is now available in the United States through FDA-approved tablets for very few specific allergens. Like allergy shots, SLIT addresses the root cause of allergies rather than simply suppressing symptoms.
How Does SLIT Work?
The immune mechanisms underlying SLIT are similar to those of allergy shots. Repeated exposure to small amounts of allergen under the tongue triggers a cascade of immune changes:
Engaging the oral immune system: The tissue beneath the tongue contains specialized immune cells called dendritic cells. When allergen is held under the tongue, these cells capture it and present it to other immune cells in a way that promotes tolerance rather than allergic inflammation.
Shifting the immune balance: Like allergy shots, SLIT shifts the balance from allergy-promoting cells toward regulatory cells that calm the immune response.
Building blocking antibodies: Treatment stimulates production of IgG4 antibodies that can intercept allergens before they trigger allergic reactions.
Training regulatory cells: SLIT increases regulatory T cells and B cells—the immune system's "peacekeepers" that prevent overreaction to harmless substances.
What Forms Are Available?
SLIT comes in two forms:
Tablets: FDA-approved tablets are available for grass pollen, ragweed pollen, tree pollen, and house dust mites. These are standardized products that have been rigorously tested in large clinical trials. The tablets dissolve quickly under the tongue and are taken once daily.
Drops: Some allergists prepare liquid drops using allergen extracts. While drops are widely used in Europe and by some US allergists, they are not FDA-approved in the United States and are considered "off-label" use. Drops may allow treatment of multiple allergens simultaneously, though evidence for this approach is less robust than for single-allergen tablets.
What Does Treatment Involve?
The first dose is given in a medical office under supervision, with a 30-minute observation period to ensure safety. If this dose is tolerated without problems, subsequent doses can be taken at home.
Daily administration: Unlike allergy shots, which require regular office visits, SLIT is self-administered at home once daily. The tablet or drops are held under the tongue for a specified time (usually 1-2 minutes for tablets) before swallowing.
Duration of treatment: Like allergy shots, SLIT should be continued for at least 3 years to achieve lasting immune changes that persist after treatment ends. Studies have shown that 2 years of treatment is not sufficient to maintain benefits after stopping: the full 3-year course is necessary for disease modification.
For seasonal allergies: Treatment typically begins 12-16 weeks before the anticipated pollen season and continues through the season, though year-round treatment may provide better long-term results.
What Are the Benefits?
SLIT offers several advantages:
Proven efficacy: Meta-analyses confirm that SLIT significantly reduces allergy symptoms and medication use. Studies show improvements in nasal symptoms, eye symptoms, and quality of life.
Home administration: After the first supervised dose, treatment can be done at home, eliminating the need for frequent office visits.
Favorable safety profile: SLIT has an excellent safety record. Serious systemic reactions are rare, and no fatalities have been reported with SLIT.This safety profile is what allows home administration.
Lasting effects: Like allergy shots, the benefits of SLIT can persist for years after completing a full course of treatment.
Comparable efficacy to shots: Head-to-head comparisons suggest that SLIT tablets and allergy shots have similar overall effectiveness, though some indirect comparisons suggest shots may have a slight edge for symptom relief.
Works in polysensitized patients: Even if your child is allergic to multiple things, treating the most clinically relevant allergen with a single-allergen tablet still provides meaningful benefit for that specific allergy.
What Are the Side Effects?
Local reactions are common and expected, particularly in the first few weeks of treatment. These include:
- Itching or tingling under the tongue or in the mouth
- Mild swelling of the lips or tongue
- Throat irritation
- Ear itching
These reactions are typically mild, resolve within minutes to hours, and often diminish over the first few weeks of treatment.
Systemic reactions are rare. The rate of serious adverse events is estimated at 1% or less, with rare cases of anaphylaxis reported. This is why the first dose must be given under medical supervision and why patients are typically prescribed an epinephrine auto-injector.
Gastrointestinal symptoms such as nausea or abdominal discomfort can occur but are generally mild.
How Does SLIT Compare to Allergy Shots?
Both approaches work through similar immune mechanisms and offer disease-modifying benefits. The choice often comes down to practical considerations and personal preference:
SLIT advantages:
- Home administration after the first dose
- No injections
- Lower risk of severe systemic reactions
- More convenient for busy families
Allergy shot advantages:
- Can treat multiple allergens simultaneously with a single injection
- Longer track record of use
- May have slightly greater efficacy for some patients
- Regular office visits ensure adherence and monitoring
Overall: Current evidence suggests that SLIT tablets and allergy shots are comparably effective for allergic rhinitis. Guidelines recommend either approach through shared decision-making based on patient preference, allergen availability, and practical considerations.
Is My Child a Good Candidate?
SLIT may be appropriate for children who:
- Have confirmed allergic sensitization through skin testing or blood tests
- Experience significant symptoms despite medications
- Have allergies to allergens for which FDA-approved tablets exist (grass, ragweed, tree pollen, or dust mites)
- Prefer home-based treatment over regular office visits for injections
- Can commit to daily treatment for at least 3 years
Age considerations: FDA-approved grass pollen tablets are approved for ages 5 and older; dust mite tablets are approved for ages 12 and older. Your allergist can discuss whether SLIT is appropriate for your child's age and situation.
Children with uncontrolled asthma should have their asthma well-controlled before starting SLIT.
What to Expect During Treatment
First few weeks: Local reactions (mouth itching, throat irritation) are most common early in treatment and typically improve over time. Some families find it helpful to take the dose with a small amount of water afterward.
First year: Symptom improvement often begins within the first pollen season of treatment, though the full benefit may take longer to achieve.
Years 2-3: Continued daily treatment reinforces immune tolerance. Adherence is important, the treatment only works if taken consistently.
After completing treatment: Most patients maintain their improvement for years after stopping. Some may eventually experience gradual return of symptoms, at which point a shorter course of treatment may be considered.
Practical Considerations
Consistency matters: SLIT requires daily administration, which can be challenging for some families. Building it into a daily routine (like brushing teeth) can help.
Storage: Tablets should be stored as directed, typically at room temperature away from moisture.
Timing around illness: Your allergist will provide guidance on whether to pause treatment during acute illnesses, particularly those affecting the mouth or throat.
Cost: SLIT tablets may or may not be covered by insurance. Discuss costs with your allergist's office before starting treatment.
A Natural Approach to Lasting Change
Like allergy shots, sublingual immunotherapy represents a fundamentally different philosophy than symptom-suppressing medications. Rather than blocking the allergic response, SLIT works with the body's natural capacity for immune learning and adaptation. The goal is to restore normal immune tolerance, teaching the immune system to appropriately ignore harmless environmental substances.
The convenience of home administration makes this approach accessible to families who might not be able to commit to regular office visits for injections. For many children, SLIT offers a practical path toward lasting relief from environmental allergies.
Questions to Ask Your Allergist
- Is there an FDA-approved tablet for my child's specific allergens?
- Would tablets or drops be more appropriate for my child's situation?
- What local reactions should I expect, and how should I manage them?
- How will we monitor my child's progress during treatment?
- What happens if we miss doses?
- How will we decide when it's time to stop treatment?
Your allergist can help you weigh the benefits and practical considerations of SLIT versus allergy shots and determine which approach is right for your family.
