Because the female endocrine system is so complex, medical experts don't fully understand the chain of events that causes PMS in some women and not others.

PMS 101 PMS Symptoms What Causes PMS?

Your Secret to Happiness at Every Age What Causes PMS?

Breast swelling and tenderness Acne Bloating and weight gain Pain - headache or joint pain Food cravings Irritability, mood swings, crying spells, depression No one knows what causes PMS, but hormonal changes trigger the symptoms.

Dr. Rossignol said caffeine may not by itself cause PMS but it may contribute to the onset of symptoms or make the condition more severe.