I have used the factor 20 in the past, but now that they have introduced the factor 50 have switched to this. I am very fair skinned and burn easily (within a few minutes) and this can see me through the day without getting burnt. I have used the factor 20 numerous times whilst on holiday snorkelling and swimming and have never been burnt, apart from the bits where I had forgotten to apply the lotion! (Which acted to prove how effective the product was on the rest of my skin where it had been applied!). It is a bit more expensive, but you really do only have to use it once a day. It does warn that if you rub your skin with a towel after swimming you need to reapply, but if you just pat yourself dry or air dry, the protection continues. Also, like a lot of lotions, beware or the necklines on white garments, it isn't as bad as some lotions, but it can leave yellow marks....Excellent product.