Can UV exposure from tanning cause itchy blotches that swell up briefly in same place each time?

Every time I go to tan in a stand-up tanning booth I get some blotchy areas on the back of one hand and that wrist that itch and swell a little. This has been happening for several years. The itching begins just moments after the UV lights turn on, some swelling gradually occurs and then it all disappears about 15 or 20 minutes after I finish my tanning session. While tanning, I can see the blotches on my skin and they appear to be darker in color than the rest of the surrounding skin. They resemble splashes of some liquid on my hand and forearm, and they begin to itch like crazy. They swell slightly, like welts, in 1/2 " diameter spots and it's all gone after a short while but each time I tan the spots and itching reappear in exactly the same places. They do not turn red. What could cause this? A reaction to something spilled on my skin years ago that still remains embedded in my skin? A fungus in the skin? Anyone have any ideas?