Warm weather entices us outside, but in lots of places, summer is mosquito season. If the mosquitoes in your area carry serious diseases like dengue, Zika or chikungunya, you should probably invest in effective commercial repellents with DEET or picaridin and use them conscientiously. If, on the other hand, the main problem is the itchy bite itself, you might be tempted to consider another approach. We have heard from a few readers that vitamin B1 (thiamine) may help keep mosquitoes from biting.
Can Thiamine Keep Mosquitoes from Biting?
Q. Mosquitoes love me. I used to go to a lake in Ontario for a couple weeks each summer. The fishing was awesome, but the mosquitoes were big and plentiful and would bite me, leaving lots of raised welts that itched like crazy.
Then my aunt (an OR RN) told all of us to start taking vitamin B1 (100 mg once a day) for two weeks before we leave for Canada. It worked like a charm. Mosquitoes would descend upon our boat and land on my bare skin and then take off without biting! I was able to enjoy fishing without being bitten once. I swear by the vitamin B1.
Topical Vitamin B1 May Work Though Pills Do Not:
A. Vitamin B1 (thiamine) has been controversial as a mosquito repellent. Many people, like you, report benefit from oral doses. However, a study found it did not keep mosquitoes from biting (Journal of the American Mosquito Control Association, June 2005). Scientists have rarely studied whether taking vitamin B1 orally is effective as a mosquito repellent. One trial we found dates back many years and reached similarly discouraging conclusions (Transactions of the St. John’s Hospital Dermatological Society, 1969).
On the other hand, a tiny pilot study recently demonstrated that thiamine hydrochloride (vitamin B1) works as a topical mosquito repellent (Biological and Pharmaceutical Bulletin, Feb. 2020).
The researchers conclude:
“This finding can be supported by future works in which a proper formulation of thiamine hydrochloride in the respective doses would be presented. One can get prolonged safe protection against insect bites.”
Why Not Use DEET?
The compound known as DEET, aka N,N-diethyl-m-toluamide, and now called N,N-diethyl-3-methylbenzamide, is the gold standard for mosquito repellents (New England Journal of Medicine, July 4, 2002). That is why we suggest using it when mosquito bites might transmit a potentially lethal disease.
On the other hand, readers have reported that DEET can kill grass and dissolve super glue. Many people are concerned that it poses dangers to children. Although DEET can keep mosquitoes from biting, so can picaridin and oil of lemon eucalyptus (Wilderness Environmental Medicine, March 2016). In fact, these topical repellents are better than DEET at protecting people from ticks, blackflies, midges and sandflies. Perhaps someday soon, topical thiamine hydrochloride will join the list of effective alternatives to DEET.