Sun screen

I went to look for some sun screen yesterday.  In Belgium I didn't have much need to buy it very often.  Here in Hendaye it has become a more regular item on my shopping list.   A 25ml bottlecomes in at around 20-30 Euro.  Thats more than my (organic) shopping bill for three to four days: more expenisive per litre than a bottle of Grand Cru!  Can somone please tell me what the secret and obviously very expensive ingredient is?  I'm suspecting it's a mixture of fear and vanity.