Methanethiol we’ve already come across at several points; two of the other main compounds contributing to ‘cheesy’ feet are propanoic acid & isovaleric acid. Propanoic acid is described as ‘pungent, sour and rancid’, whilst isovaleric acid attracts similar plaudits: ‘cheesy, rancid & fermented.’ The presence of isovaleric acid is actually the result of a bacteria also found in some strong cheeses.