In other words, the exposure must precede the onset of the disease. Clearly, if the onset of the disease is before the exposure, one cannot point to the exposure as having caused the disease. This is not to say, however, that a temporal relationship by itself is sufficient to prove causality. For example, if one developed a neuropathy after drinking one ounce of whiskey, we would not assume that person had an alcoholic neuropathy because the amount of alcohol consumed was far too little to cause such a disorder. Thus, even though there is temporal eligibility in this case, we would search for a more reasonable cause.
Latency refers to length of time between chemical exposure and the onset of symptoms.
This is especially important in considering whether or not a chemical caused a cancer. We can be fairly certain, for example, that a lung cancer which presents two days after smoking one's first cigarette is due to some other carcinogen. Brooks, S.M., Gochfeld, M., Herzstein, J. et al. Environmental Medicine . The Henle-Koch postulates revisited.