I have heard there is something in sunscreen that can mimic a hormone, could this be causing the problem?
I feel that anything is possible to trigger a Migraine attack. If we are triggered off of foods, smells, noise and light, why not off of something we put on our body?
Is it possible you are triggering from too much sun and not the sunscreen itself? Just a thought.
Search the web for more natural sunscreens, maybe with less chemicals. I know of one called Propaline that is sold at Bath and Body Works....or ask your doctor, maybe he/she is aware of a brand to try.
Good luck in your search.
There are three types of sunscreen: organic chemical compounds which absorb UV, inorganic particulates which deflect UV, and organic particulates which do some of both. The organic chemical compounds are increasingly controversial because of reported estrogen-mimicking effect, which could certainly be responsible for your migraines. Try sticking with the inorganic particulate sunscreens such as those which are exclusively based on zinc oxide and titanium dioxide. These are a lot more common than they used to be.