I am a 22-year-old white male. I just woke up this morning with about 8 rusty-colored spots on the back of my right wrist. There is also one small spot in between my index and thumb, which sounds like the most common location according to many of these posts.
So many of the experiences posted sound similar to mine; I'll share mine, and hopefully it will help figure out what's going on.
I have been spending a lot of time in a fitness center the past month. That increases the chance of getting a fungal skin condition, but the spots do not look like a fungus. They look like age spots, and they definitely formed overnight. Since I have been lifting a lot, I have dramatically changed my diet to a heavy dose of proteins. More specifically, I have been eating a lot of eggs, cottage cheese, and tuna. One previous poster mentioned proteins and tuna as possible contributors.
Although I am pale, I do not believe the spots were caused by the sun, as I have not spent significant time out side since the summer. I have not handled mangos, lemons, limes, or any other citrus fruit lately, but it might be worth mentioning that my house has seemed bombarded with fruit flies for a couple weeks. They are mostly after bananas though.
As a college student, this past week has been filled with stress and irregular sleeping patterns (one all-nighter writing a paper). These issues were mentioned by a couple previous posters.
Many previous posters mentioned alcohol, and some mentioned cigarettes too. This sounds like the most probable cause for me, because between the past two nights, I have consumed between 20-25 drinks (mostly beer). I also had a handful of cigarettes too. Over the last two evenings I took many NSAIDs (Ibuprophen) to help with headaches and hangovers. The warnings on the bottle to not advise combining NSAIDs with more than 3 drinks. If the discolored spots are caused by internal capillary rupture, then the NSAIDs (especially combined with alcohol) could likely be the cause.
The bottom line is that I have been very rough on my body this past month, week, and especially the past couple evenings. I'm not sure if it's the alcohol, proteins, sleep habits, NSAIDs, or some "perfect storm" of all of them combined. I'm going to tone down on the partying for a little while and add more fruits and vegetables to my diet, and hopefully, that will help. Please post information if any of you find out a single cause for this.
p.s. I also have a strange condition with my ears. I have heard people call it "red ear syndrome" in online threads like these. It is very mysterious but is related (for me, at least) to many factors such as stress, hour of the day, alcohol consumption, touching the ears, and others. I just thought I'd mention this because many of the causes sound like the causes of the hand-spots. let me know if any of you also have "red ear syndrome" too.