Some studies suggest that taking thiamine (Vitamin B1) 25mg to 50 mg three times per day(orally) is effective in reducing mosquito bites. Thiamine produces a skin odor that is not detectable by humans, but is disagreeable to pregnant mosquitoes (Pediatric Clinics of North America, 16:191, 1969). It seems to be especially effective for those people with large allergic reactions to bites. When taken orally, thiamine takes about 2 weeks before the odor fully saturates the skin, however, with the patch, it only takes two hours.