Which factor does NOT influence the blood alcohol concentration (BAC) of an individual?

The factor that does not influence an individual's blood alcohol concentration (BAC) is family history of alcohol use. BAC is primarily affected by measurable physical and situational factors at the time of alcohol consumption.

A person's weight plays a crucial role in how alcohol is metabolized and absorbed in the body; generally, individuals with lower body weight will have a higher BAC after consuming the same amount of alcohol as a heavier person. The type of drink consumed also significantly impacts BAC, as different beverages contain varying amounts of alcohol, affecting the total volume of alcohol in the bloodstream. The time of day can influence BAC because it may correlate with drinking patterns and the body's metabolism over time, including the rate at which alcohol is processed.

In contrast, family history of alcohol use does not have a direct effect on an individual’s BAC level at any given moment; rather, it might influence a person's drinking habits or attitudes towards alcohol, but it doesn’t affect the biochemical process that determines BAC at the time of testing.