Why do some people consistently overheat at night while their partners sleep comfortably under identical conditions? The answer involves several interacting factors.
Metabolic Rate
The most fundamental cause is metabolic rate. Your resting metabolic rate determines how much heat your body generates at rest. People with higher metabolisms produce significantly more body heat. Since you cannot turn your metabolism down at night the heat has to go somewhere. Under insulating bedding it has nowhere to go except back against your skin.
Hormonal Factors
Hormones are among the most common causes of running hot at night. Estrogen plays a key role in temperature regulation through its effect on the hypothalamus. As estrogen declines during perimenopause and menopause the hypothalamus becomes hypersensitive to small temperature changes, triggering heat-dissipation responses to tiny fluctuations. Thyroid hormones, cortisol, and reproductive hormones all influence body temperature during sleep. This is why women are significantly more likely to be hot sleepers than men and why the problem often intensifies in the 40s and 50s.
Body Composition
Muscle tissue generates more heat than fat tissue. People with higher muscle mass and lower body fat tend to run warmer during sleep. Regular exercise increases muscle mass and can make people hotter sleepers over time, even as it improves overall sleep quality.
Medications
SSRIs, SNRIs, blood pressure medications, hormone treatments, and some diabetes medications commonly cause night sweating and elevated body temperature during sleep. If you started running hotter around the time you started a new medication this connection is worth discussing with your healthcare provider.
Sleep Environment
The bedding itself contributes significantly. Insulating bedding creates a feedback loop where trapped heat raises skin temperature which generates more heat which raises skin temperature further. Even a mild hot sleeper can become a significant one under the wrong bedding.
The One Variable You Can Easily Change
You cannot change your metabolism or your hormones through bedding choices. But you can change whether the heat your body generates is trapped against you or drawn away. A nylon cooling blanket changes this variable directly. See The Cloud here.