If you cant stand long sleeves, sunscreen with titanium oxide or zinc oxide is best - it should turn your skin several shades lighter than it is. Stay away from PABA sunscreens - they are very high on the sensitivity list, and they usually need reapplication.

I am EXTREMELY sensitive to the sun - I actually have an allergic reaction to UV light itself if it hits my arms. I break out in this bad bubbly weepy very itchy nasty rash that leaves white spots for years afterwards.

The stuff I use lets me stay out in the sun for 10 hours (on 2 applications or so) without sunburn, rash or any ill effects, Once it's on I never even notice it's there, and it seems that I sweat right through it. I have only very faint tan lines on my upper arms, I use this stuff religiously everytime I am out in the sun. I use the kid version because it's less likely to have irritants of any kind in it - something my rash prone skin does not need.

http://www.solsunguard.com/kindersport.html