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Normal human body temperature is 37 degrees Celsius. The human body has three types of sensory receptors in the skin: pain receptors, heat receptors, and cold receptors. Heat receptors start to perceive heat above 30 degrees Celsius (and up to around 45 degrees, where pain receptors take over). Cold receptors perceive cold when temperature drops below 35 degrees. As you can see, there is a 5-degree overlap zone that will trigger both heat and cold receptors. You feel cold more acutely than you feel heat because your body has 4 times the number of cold receptors as heat receptors. Many of these are located in the face, ears, hands, and feet. Cold receptors stop functioning below 5 degrees Celsius, when you stop feeling cold and start feeling numb. Your core body temperature can vary slightly, depending on hormonal changes and health. When your temperature exceeds 37 degrees (98.6% Fahrenheit) your blood vessels will dilate, allowing more blood to reach the surface of the skin to be cooled. When your temperature drops, blood vessels contract to conserve body heat. As you regularly experience this sensation, your body will become more efficient at thermoregulation (the temperature control process). Part of the difficulty of getting in a cold shower (particularly in the morning when you have been in bed) is that the shock is exacerbated because your surrounding environment was previously warm. If you lower the temperature of your environment the cold water will be less shocking. Turn the thermostat down a degree or two. This will even save you money in the winter. Have a fan in the bathroom or bedroom. Increased circulation of air under 37 degrees will accustom your body's cold receptors to being activated. Don't bundle up as tight at night. This can be especially helpful if you are having trouble with cold morning showers. The warmer you bundle up, the colder the shower will feel! There are times when the cold can feel good, like when you jump into a pool on a hot summer day or drink a cold beverage after strenuous sports activity. This is because your body is elevated to over 37 degrees and is struggling to lower its temperature. If you raise your body's temperature, you can not only make cold water easier to adjust to, but you can also make it refreshing. Consider high-intensity exercise before a cold shower. Interval or circuit training is especially effective. Your cold shower will have the added benefit of helping your muscles recover!
Understand why you feel hot and cold. Understand how your body reacts to temperature. Lower your environment's temperature. Raise your core temperature to make cold feel better.