Vitamin B1 for Mosquitoes: Does It Really Keep Them Away?

This page is general information, written by our founder. It is not medical advice.

Where the Thiamine Mosquito Idea Came From

In 1943, a Minnesota pediatrician named W. Ray Shannon published a short report on 10 children and 3 adults he had given B1, mostly to ease itching from bites. Families told him afterward that mosquitoes left them alone, and he concluded that B1 could keep bugs away from the inside. Doses ranged from 10 to 120 milligrams, one to four times a day. There was no comparison group, and the results were what patients and parents reported from home (Shelomi, 2022).

A theory soon followed: that the body releases B1, or a sulfur-containing breakdown product of it, through the skin, giving off an odor that lowers mosquito attraction. It was a reasonable guess for its time. It turned out not to be true.

What Happens When Taking Vitamin B1?

The first proper clinical trial came in 1969, and its title gave away the answer: “Vitamin B1 is not a systemic mosquito repellent in man.” In one experiment, adults took 50 milligrams three times a day for three days, and the insects actually probed them sooner. In a double-blind, placebo-controlled test, people who took 200 milligrams three times over two days sat in a room with 100 hungry mosquitoes. The B1 group was bitten slightly more, though not by a significant margin (Shelomi, 2022).

Why would anyone expect vitamin B1 to work in the first place? A mosquito finds people mostly by carbon dioxide, body heat, and skin odor. For a pill to help, it would have to change that odor enough that mosquitoes turn away. That is exactly what researchers tested.

Later studies used larger groups, several species, and stronger controls. They consistently found that oral B1 did not change how attractive people or their skin odors were to mosquitoes. Skin patches containing 300 milligrams of B1 failed too.

The odor theory did not hold up either. Large doses raise B1 levels in sweat, but only to less than one microgram per milliliter, and the sulfur part of the molecule does not break off along the way. In 2022, a scoping review in the Bulletin of Entomological Research summed it up: thiamine does not repel biting insects of any species, at any dose, over any period of time, in any form (Shelomi, 2022).

The CDC agrees. Its Yellow Book, the guide doctors use in travel medicine, says that vitamin B pills and garlic do not prevent bites (CDC Yellow Book).

Why People Still Search for a Pill

Type “B1 to repel mosquitos” into Google and you will find plenty of articles, online reviews, and pest-control blogs that recommend it. If it does not work, why does the idea last? The review offers a few gentle explanations (Shelomi, 2022):

• Bite reactions change on their own. Swelling and itching can fade within two hours, delayed reactions can come a day later, and repeated exposure over a summer can dull a person’s reaction. Fewer itchy bumps can feel like fewer mosquito bites.
• The early reports were easy to find, and the corrections were not. Many of the negative studies sit behind paywalls, while positive claims circulate freely.
• The idea keeps getting repeated. In a 2020 Australian survey, 27 percent of pharmacists thought B1 keeps bugs away.

None of this means people were being foolish. A vitamin B tablet is cheap and easy, and the story behind it is old. It just has not passed the test. The same goes for other vitamins and for garlic.

Health Risks of Relying on Pills

B1 itself is generally low risk at ordinary amounts. The real health concern is what happens when someone trusts a pill instead of real mosquito protection. In many parts of the United States, bites can spread West Nile virus, and travelers may face dengue, Zika, or malaria. For prevention, the CDC’s travel guidance relies on tested repellents, protective clothing, and netting instead (CDC Yellow Book).

If you develop a fever, a spreading rash, or flu-like symptoms after bites, especially after travel, see a doctor and mention where you have been. Public health agencies treat these infections seriously, and so should we. Your health matters more than any home remedy. A pharmacist or other health professional can help you choose a mosquito product for your trip.

A Note from Russ

I started Tarsul in 2010 around an old pairing of sulfur and cream of tartar, and the idea that sulfur and B1 keep bugs away has followed products like ours for a long time. Older pages on this site leaned into it. Having read the evidence, I would rather tell you plainly: no pill, including ours, has been shown to repel mosquitoes. If you are outdoors where bites matter, please use a tested product.

What to Use Instead

The CDC recommends EPA-registered repellents, which have been tested for effectiveness. To prevent mosquito bites with a plant-based product, look for OLE, PMD, or 2-undecanone. Synthetic options are DEET, picaridin, and IR3535 (CDC). Do not use OLE or PMD on children under 3.

For protection on a hike or a trip abroad, choose a product with an EPA number. Good mosquito defense also means long sleeves at dusk, sound window screens, and emptying standing water each week. For a side-by-side comparison of each repellent type, a simple routine, and where sulfur genuinely helps with ticks and chiggers, see our guide to natural mosquito repellent for skin.

Tarsul is a daily mineral supplement, two ingredients, cream of tartar and MSM, made in San Diego since 2010. It is not an insect repellent. Read about cream of tartar and MSM, or see Tarsul capsules and powder.

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