Causes of hot and cold flushes on the back?

Nerve dysfunction: hot or cold sensations are controlled by nerves in the skin. A variety of underlying issues can cause this sensation. Alcohol related neuropathy, diabetes, hormonal changes, nerve damage, and MS. It might be wise to see a DR for a full workup. Keep a diary of when it happens and anything that was going on at that time: Diet, exercise, period, sleep, anxiety, alcohol/drug consumption, etc.