Chilling
Some people have a poor circulation either at the arterial level or poor perfusion into the capillaries. If the ambient temperature drops the tissues in the extremities may not get enough nutrients and oxygen and so begin to break down into an ulcer or necrose and go black. This is usually common in parts of the foot where there is most pressure such as the ends of the toes and under the ball of the foot which will first of all look cyanosed (blue). This should be seen by a Podiatrist as early as possible and usually is reversible provided it hasn’t been neglected too long.
If in doubt send a photo via our Foot app and one of our team will advise you further.