Where I live on the edge of the Peak District we’ve recently had a burst of midges, resulting in a mass biting that led to Tesco selling out of creams and lotions for treating bites. That didn’t bother me (although it really bothered my wife), because I hardly ever get bitten. Why might that be? According to James Logan from Rothamsted Research, the answer (for Culicoides impunctatus at least) is probably that I smell funny .
Comparing human odour extracts, several compounds were found to differ between those bitten and those not. The repellant activity of some was confirmed in behavioural assays. Two particular compounds showed activity: geranylacetone (PB) and 6-methyl-5-hepten-2-one (PB), both of which can be found in the insecty parts of PheroBase (hence PB), a pheromone database.
An excellent piece of work. Similar experiments have also been fruitful on mosquitoes .
 Logan JG, Seal NJ, Cook JI, Stanczyk NM, Birkett MA, Clark SJ, Gezan SA, Wadhams LJ, Pickett JA, Mordue AJ. Identification of human-derived volatile chemicals that interfere with attraction of the Scottish biting midge and their potential use as repellents. J Med Entomol. 2009 Mar;46(2):208-19. PMID:19351071
 Logan JG, Birkett MA, Clark SJ, Powers S, Seal NJ, Wadhams LJ, Mordue Luntz,AJ, Pickett JA. Identification of human-derived volatile chemicals that interfere with attraction of Aedes aegypti mosquitoes. J Chem Ecol. 2008 Mar;34(3):308-22. Epub 2008 Feb 29. PMID: 18306972