A variety of factors causes caffeine sensitivity, such as genetics and your liver's ability to metabolize caffeine. A caffeine allergy occurs if your immune system mistakes caffeine as a harmful invader and attempts to fight it off with antibodies.

Can caffeine suddenly affect me?

People who regularly consume caffeine can build up a tolerance to its effects. Some people may even develop a slight physical or behavioral dependence on caffeine. Those who abruptly quit caffeine after regularly consuming it may experience unpleasant symptoms, such as headaches and irritability.

Why does caffeine affect me as I get older?

As you age, your body's ability to break down drugs and natural products is reduced. However, it turns out that caffeine is not affected; in fact older folk break caffeine down slightly faster than young people.