What Causes Brown Spots Between The Thumb And Knuckle?

i have 2 big round dark brown color mark on my left hand between the thumb and knuckles i got this mark about a month back, i use laptop all day for work like 10 hours a day i am not sure if its coz of the heat from laptop or something else as i got a small little mark recently 3-4 days back on my right hand on the same place on right hand but its very small mark, i was using propysalic NF but it dint then i was using Eldoquin 2% it dint help recently i was using lobate GM as all these were refered by dermatologists but dint help. pls help me the sight of the mark makes me feel bad.