IR3535
3-(N-Butyl-N-acetyl)aminopropionic acid, ethyl ester
What is IR3535?
IR3535 is a synthetic amino-acid derivative that's been Europe's quiet workhorse repellent for over 30 years. At 20% it provides roughly 6–8 hours against both mosquitoes and ticks, with one of the gentlest safety profiles of any synthetic.
When to choose it: Families and sensitive skin: long protection with minimal irritation risk. A strong tick performer.
Synthetic repellent also known as ethyl butylacetylaminopropionate (EBAAP). Common in Avon Skin-So-Soft Bug Guard and similar products.
The evidence
Moderate-duration protection; often combined with sunscreen in consumer products.
Mosquito protection by concentration: IR3535
Complete protection time (dark = lower bound, light = upper bound) on the same 12 h scale used across the site. Modeled from published dose-response data in our research library.
- Evaluation of the efficacy of 20% IR3535 with a sustained-release formulation and 25% DEET against mosquitoes in a field setting in Ghana2025Field TrialWell-supported evidence
Field human-landing-catch evaluation of a sustained-release 20% IR3535 formulation versus 25% DEET against wild mosquito populations in Ghana.
- Field evaluation of the efficacy and persistence of insect repellents DEET, IR3535, and KBR 3023 against Anopheles gambiae complex and other Afrotropical vector mosquitoes2004Field TrialDefinitive evidence
Large topical field trial in Burkina Faso directly comparing skin-applied DEET, IR3535, and KBR 3023 (picaridin) against wild malaria vectors, with over 49,000 mosquitoes collected (~95% Anopheles gambiae complex).
- Laboratory and field evaluations of the insect repellent 3535 (ethyl butylacetylaminopropionate) and deet against mosquito vectors in Thailand2001Field TrialWell-supported evidence
Paired laboratory arm-in-cage and field human-landing topical evaluations of IR3535 versus DEET against multiple mosquito vectors in Thailand.
Common misconceptions
Myth: “If it were any good, it would be famous.”
Reality: IR3535 is famous in Europe, where it has anchored Merck-developed repellents since the 1980s. Its low profile in the US is marketing history, not evidence.
Myth: “All 'gentle' repellents are weak.”
Reality: IR3535 at 20% posts protection windows in the same range as mid-to-high DEET, while being mild enough for daily family use.
Regulatory notes
EPA SRS-registered active. Not a FIFRA 25(b) minimum risk active.
The best products built on it
All products using it
- Bullfrog Mosquito Coast Sunscreen + Insect Repellent SPF 50
20% · Active repellent
- Skin So Soft Bug Guard Plus IR3535 Expedition Aerosol Spray SPF 28
20.07% · Active repellent
- Bug Repell IR3535 10% Lotion
10% · Active repellent
- Bug Repell IR3535 20% Spray
20% · Active repellent
- GoReady
20% · Active repellent
- Superguard 3535 Insect Repellent (SPF 20)
20% · Active repellent
- Cutter All Family Insect Repellent
20% · Active repellent
- Skin So Soft Bug Guard Plus IR3535 Gentle Breeze SPF 30 Lotion
7.5% · Active repellent
- Skin So Soft Bug Guard Plus IR3535 Expedition SPF 30 Pump Spray
19.6% · Active repellent
- Zevo On-Body Mosquito and Tick Repellent Aerosol Spray
20% · Active repellent
- Zevo On-Body Mosquito and Tick Repellent Lotion
20% · Active repellent
- Zevo On-Body Mosquito and Tick Repellent Pump Spray
20% · Active repellent
Frequently asked questions
How does IR3535 compare to DEET?
At equal concentrations, broadly comparable against mosquitoes and at least as good against ticks. Its 2025 Ghana field trial pitted 20% IR3535 against 25% DEET with competitive results.
Is IR3535 natural?
No, it's synthetic, though modeled on the natural amino acid β-alanine. It's EPA-registered as a biopesticide.