Hands and feet are the first places the body economises on heat. When the core needs protecting, the small vessels in the fingers narrow and the extremities cool down. That is normal, useful and mostly invisible. It becomes a signal when it happens in a warm room, when it happens to only one hand, or when it is new.
What it feels like from inside
Fingers that go white or bluish and then flush red as they warm, toes that stay cold under a blanket, a numb or clumsy feeling when opening a jar in a cold kitchen. Some people notice their partner comments on it before they do.
The ordinary explanations
Low body weight, smoking, caffeine, a cold house, and simply being someone whose vessels react strongly to temperature. Women and thin people are cold-handed more often, and it usually means nothing more than that.
The explanations worth knowing about
An underactive thyroid slows the whole engine and makes people feel cold everywhere. Low iron does something similar. Some blood pressure tablets and migraine medicines narrow small vessels as a side effect. Colour changes confined to one hand, or fingers that stay white for a long time, deserve a proper look rather than another pair of gloves.
A simple way to observe it
Note when it happens, whether both sides match, and how long the colour takes to come back. Photographs of the colour change are more useful to a clinician than a description, because the episode is usually over by the time of the appointment.
What to raise, and what not to wait on
Worth mentioning at a routine appointment: new cold sensitivity, colour changes in the fingers, or cold hands alongside tiredness, weight gain or dry skin. Worth raising promptly: a finger that stays white or blue and painful, or a sore on a fingertip that will not heal. Most cold hands are just cold hands. The change is what matters.