What cosmetic category do you find the most challenging to apply or use effectively? Share one tip or trick you've learned for mastering products in this category.

I've been making sunscreens and have won many awards for my sunscreens I've tested every major brand or worked on every brand imaginable. Sunscreens, hands down is the hardest most challenging catergory. There are so many misconceptions. People ask me what is the best sunscreen, and tell them the same thing: 1) Use a value between 30 and 50 2) Reapply... Reapply.... Reapply. You do not use enough and if you miss a spot on the first application more than likely you will get it one the second. 3) You do not use enough sunscreen so don't be stingy. 4) Every 80 minutes if you are wondering if you need to reapply... then do it!