Problems with blood vessels. We call it vegetative-vascular dystonia, but after suffering with it and going to different doctors (including those not in Russia) I realized (well, it is written everywhere) that this is a universal excuse for doctors in the post-Soviet space. IRR is 100,500 different deviations, and what exactly you have is unknown.
I suffer from this too. One of the reasons may be a sedentary lifestyle, if you constantly sit at the workplace / subway / bus, etc., then try to play sports, walk if possible, you need to add activity :)
The reason may be a decrease in blood circulation in the upper extremities. Usually the feet are cold too.
Maybe Raynaud's syndrome?
What to do?
If it's not Raynaud's syndrome, then it will be enough to quit smoking if the patient smokes, wear gloves , quench your hands - do contrasting baths (put your hands in cold and hot water).