Ask Larry:

Question: I’ve been reading on chemical-free ways of keeping mosquitos at bay. Will brewers yeast prevent mosquito bites? If so, how much should you take and what is the best brand to buy? Also, are there any side effects?

Larry’s Response:

I’ve used it and found that it helped a lot.

How much? A couple of tablets prior to going outside. Repeat every 4 hours.

The B vitamins in Brewer’s Yeast makes perspiration taste bitter. Mosquitos like sweet. I’ve also used Thiamine tablets for the same reason.

I won’t say that these products prevent bites. However, I think they reduce the chances. Some mosquitoes might not mind the taste. Regardless, it is safe and worth trying.
You really can’t take too much.

Be aware, though, over time, the smell of the vitamins can coat the skin.
Practically any brand is fine. I’d personally stay away from the cheapest.