It sounds as if you may have a skin condition from which I also suffer! It's known as polymorphous light eruption - thankfully abbreviated to PMLE. It's very important for you to consult a board certified dermatologist to determine whether PMLE is what you have, and not a more serious sun sensitivity condition with internal complications such as lupus. Definitive diagnosis may require a skin biopsy.
PMLE is a sun sensitivity condition that causes you to develop itchy bumps or blisters on areas that have been exposed to strong sunlight - typically the backs of the hands and the arms. It is more likely to develop at the beginning of suummer or after your first inetense sun exposure of the season, and it may improve as the summer progresses and your skin becomes less sensitive to the sun. Sun protection is important for all of us, especially since the thinning ozone layer is exposing us to far more of the sun's damaging ultraviolet radiation than even a generation ago - with a consequent explosive increase in skin cancers. If you suffer from PMLE, sun protection is even more important; the condition is harmless but quite a nuisance and can be unsightly.
I recommend that you wear a broad spectrum sunscreen protecting you from the sun's ultraviolet UVA and UVB rays. Apply the sunscreen, which should have an SPF of at least 30, to all exposed areas of your skin every day. I, and many of my patients, use a chemical-free medical-grade mineral powder sunscreen which is recommended by the Skin Cancer Foundation and provides excellent, long-lasting sun protection. It's called ColoreScience Sunforgettable, and it's available from dermatologists' offices. A prescription cortisone-type cream will treat the rash of PMLE. I like to use Locoid Lipocream because it also provide excellent skin rehydration; skin tends to develop a leathery texture when affected by PMLE. Yur dermatologist can discuss these and other treatment options with you.
Hope this helps!