Possibly - I would normally just wear a lightweight short sleeved jersey, though. I have some arm screens now which are SPF 50. Very thin and supposed to keep you cool, but not used them in hot conditions yet.
Here are some tips I've relied on when it's been hot:
If you are feeling the heat, and are wearing a cycling cap, fill it with water and put it on (I'd not use my drinking water supply for this, but if you are filling bottles at the same time then you can do this). Also, you can fill your shoes with water then put them on, splash your face with cold water. Also at controls, you could take a minute to wash the sweat out of your hair, hat, helmet over time salt builds up and then suddenly finds its way into your eyes. This is not pleasant. I've been unable to see where I'm going when a sudden downpour occurs after sweating in a helmet all day, washing all the salt out onto my face.