With the arrival of mosquito season—and, consequently, the increase in bites and a persistent buzzing that disrupts sleep—there’s no better time to understand our insect enemy. A great resource for this is The Mosquito: A Human History of Our Deadliest Predator by Timothy G. Winegard.
Mosquitoes have six "needles". Two function like electric knives to cut the skin, two retractable ones create a path for the proboscis (its sucking mouthparts), one extracts three to five milligrams of blood, and the sixth injects saliva containing anticoagulants. These anticoagulants prevent blood clotting but also cause swelling and allergic reactions. Perhaps more intriguing is that Jurassic mosquitoes and sandflies had a symbiotic relationship with various viruses, making them natural predators of thin-skinned and feathered dinosaurs.
"With their lethal weapons, insects and their stings were the apex predators in the food chain and could transform the fate of dinosaurs, just as they can shape our world today."
Unfortunately, their reign of terror continues. According to the WHO, vector-borne diseases account for more than 17% of all infectious diseases, causing over 700,000 deaths annually. Among mosquitoes, the notable include:
- Anopheles, the malaria transmitter, is responsible for approximately 249 million cases and the bulk of annual deaths (608,000).
- Aedes, the dengue vector, is the most widespread viral infection, with an estimated 96 million symptomatic cases and 40,000 deaths in 132 countries annually.
- Other mosquito-borne viral diseases include chikungunya, Zika, yellow fever, etc.
Given these concerning statistics, a comprehensive approach adopting individual measures, e.g., repellents containing Icaridin or DEET, and societal actions, including vector control and education, are the best approach to evidence-based measures. To my surprise, there is a persistent myth that vitamin B1 (thiamine) supplements act as "natural" repellent — something that is not the case.
What mosquitoes desire
The authors of “The Fantastic World of Mosquitoes” note that different species of mosquitoes react to various stimuli, but there are some common attractants that will put a target on you.
- Emitting a greater amount of carbon dioxide (CO₂) very common when you are doing some other activity that accelerates your breathing.
- Using floral or fruity fragrances.
- A higher skin temperature, since many mosquitoes are attracted to areas of the body that release heat.
- High humidity, since many mosquitoes are attracted to perspiration.
- Finally, wearing dark clothing retains heat and provides mosquitoes with dark places where they are less visible.
However, this does not fully explain why some people are bitten more than others. To explore this question, consider a review article published in Current Research in Parasitology & Vector-Borne Diseases, in which the authors highlight that anthropophilic mosquitoes—those that prefer feeding on humans—use humidity, heat, and visual and olfactory stimuli to navigate, land, and locate food.
These mosquitoes can also detect kairomones - chemical signals mediating interactions between species, benefiting only the recipient. In the human-mosquito relationship, kairomones such as carbon dioxide, lactic acid, acetone, and ammonia help mosquitoes detect and distinguish humans from other animals.
Although all humans produce kairomone, the amount lost through the skin varies between individuals. For example, CO₂ release is influenced by body mass, metabolism, and respiratory activity.
Besides species-related differences in preference and aggression, other factors determining whether mosquitoes target a particular person are their proximity to a target and individual differences in kairomone intensity and environmental conditions that affect the dispersion of these chemical signals
The authors conclude that human susceptibility to mosquitoes depends on environmental factors, mosquito-related traits, and human characteristics—including, perhaps, dietary components.
The Thiamine Myth
Thiamine is a water-soluble vitamin that aids energy production, metabolism, and “brain health.” A lack of vitamin B1 causes beriberi, a disease described over a thousand years ago, linked to B1 deficiency in the 19th century. [1]
And before anyone asks, let’s be clear: you don’t need to supplement with vitamin B1 just because your wellness coach says it’s good for you. Like most B vitamins, this vitamin is found in a wide range of foods, including eggs, dark green leafy vegetables, whole grains, meats, and liver. The best way to obtain these vitamins is through a balanced diet.
Given that there is perhaps a dietary component to being a susceptible human target, it is not a great leap to consider thiamine as a potential natural repellent. Dr. W Shannon suggested as much in a 1943 article, "Thiamin Chloride: An Aid in the Solution of the Mosquito Problem.”
In the article, Shannon compiled 10 case reports in which he administered high doses of thiamine hydrochloride to patients suffering from mosquito bites and the itching they caused.
I bring you two of his case reports.
Case 3: "An adult woman, constantly tormented by mosquito bites, took 120 mg of thiamine hydrochloride in the morning. That evening, she worked outdoors until dark without being bitten. By maintaining high doses, she remained mosquito-free throughout the summer. When bites returned, she resumed 80 mg daily for a week before tapering to 10 mg. After skipping doses for a few days, mosquitoes became a nuisance again, but increasing back to 80 mg restored the supposed protection.”
Case 8: "A seven-year-old girl was unable to swim in the lake near her home due to mosquitoes. She had numerous lesions typical of mosquito bites. She was prescribed 80 mg of thiamine hydrochloride that day and 10 mg the following day. Two months later, her mother reported that she had been swimming in the lake daily without any issues with mosquitoes."
Shannon concludes that thiamine hydrochloride, when administered in the appropriate dosage, either orally or by injection, can reduce the risk of mosquito bites in three ways: by acting as a repellent, preventing mosquitoes from approaching, by significantly decreasing post-bite itching, and by minimizing and preventing lesion formation.
Shannon's article has glaring weaknesses, drawing conclusions from isolated cases and, perhaps worse, relying on extremely high doses of thiamine hydrochloride without apparent concern for potential adverse effects. Despite these limitations, Shannon’s claims remain influential.
This was evident in a 2020 study published in Pharmacy, in which the authors surveyed Australian pharmacists using a self-administered questionnaire to assess their knowledge of travel health, covering common illnesses, management, prophylaxis, and first aid for travelers. A total of 208 pharmacists completed the assessment.
Only 56 participants (27% of the sample) correctly identified that "Oral vitamin B1 is not effective in reducing mosquito bites."
Studies have refuted the supposed protective effect of vitamin B1, including one published in the Journal of the American Mosquito Control Association. In this study, the authors describe two experiments.
In the first, each of the 23 participants underwent an analysis of their attractiveness to mosquitoes—although the specific measurements were not recorded. They were subsequently divided into two groups: the treatment group received B-complex pills with vitamin C, while the placebo group received only vitamin C.
At the end of the fourth week, participants rubbed a glass vial between their hands for two minutes. The vial was then placed in a cardboard box containing 28–32 female Anopheles stephensi mosquitoes, and the researchers counted how many mosquitoes landed on the glass vial over the next two minutes.
While the number of landings was influenced by the individual handling the vial, the B vitamin treatment did not outperform the placebo.
The second experiment followed the same design as the first but with some modifications: the number of participants was reduced to 17, the intervention changed to vitamin B1 alone (at a different concentration), and a second glass vial was introduced. This additional vial was also rubbed for two minutes and contained hot water. While mosquito landings were strongly linked to the hot water, vitamin B1 had no effect.
Consistent with these findings, a scoping review published in the Bulletin of Entomological Research concludes:
"To summarize: there is nothing in the chemical metabolism of thiamine that suggests it could act as a repellent, nor justifies the very high doses used in the articles I reviewed ... The use of thiamine as a systemic repellent is pharmacologically implausible. However, there is a possibility that it could alleviate the symptoms of the bite. Some authors have observed, in uncontrolled experiments, that it appears to reduce symptoms at the site of the bite; however, controlled clinical trials have shown this use to be ineffective."
I couldn’t say it better.
[1] Beriberi has two forms: wet beriberi, which affects the cardiovascular system, and dry beriberi, which causes peripheral nerve degeneration and muscle weakness.
