I'm over 70, and for the past 4 years or so I have been getting 'bruises' on my hands and arms, except that they're not the kind that you get if you knock yourself against something hard. They are called senile purpura, and they are purplish 'bruises'. They are caused by subjecting the hands and arms to stress, e.g. lifting a heavy object, or maybe by using hand tools (hedge clippers, screwdriver, hammer, etc.). They occur mostly in people over 60 years old, hence the 'senile' name. They are harmless, and fade after a few days. Is this what you have?