1. Biological Տҽ×.
Biological Տҽ× is a factor affecting BAC, as because there are differences on body water content for women and men.Male body is composed of 55 - 65% of water and female body composed of 45- 55% water. So alcohol is more diluted in males.Also, males have higher levels of an enzyme called gastric alcohol dehydrogenase,this aids in the metabolism of alcohol. So, blood alcohol concentration varies in men and women if they drink same amount of alcohol.
Body weight is a factor affecting BAC, the lower body weight makes for a higher concentration of alcohol in the body.A person who weighs less will have lower amounts of body water, so dilutive effect of alcohol is less.
BAC is not affected by alcohol tolerance. Long term alcohol drinkers develop tolerance to alcohol. This is because the liver become more efficient in breaking down alcohol. So they need to drink more amounts to get the same intoxication effect.
4.Time spent drinking.
This is a factor affecting the BAC. If you drink faster, quicker BAC will reach peak.
Answer is, Alcohol tolerance.