My 3 simplest answers are: pH, evaporation and detergent-based body washes/soap.
Skin lives comfortably at a pH of 4.5 to 5.5. Typically, water has a pH of 7+ and body washes may be as high as 9. The higher pH washes away oil and debris but will cause drying. Your skin will return to it’s norm of 4.5 to 5.5, eventually, after showering, but it will take some time. In the interim, it may feel dry.
Evaporation is another issue; say the phone rings and you do a quick dry and skip the moisturizer–ouch! The little water droplets left on your skin slowly evaporate and take your natural moisture into the air along with them (here we are dealing with H2O and oxygen). Your skin feels dry because the cellular matrix, similar to a honeycomb, is dry and empty and starts to feel itchy.
Detergents (aka surfactants, SLS) are found in a lot of body washes and soaps. Detergents are able to bind to both oil and water. This accounts for suds and their ability to remove dirt from your skin. However, along with dirt they also remove oil. Over time, this will cause your skin to become less supple and lose it’s ability to prevent water loss. And, if you are showering twice a day, you are doubling these effects and your skin will eventually appear dry and flaky.
The solution, like the cause, is threefold. To regulate pH, use products that are as close to your skin’s pH as possible. To combat the effects of evaporation, simply apply moisturizer to slightly damp skin. The third part of the solution is to avoid harsh detergents in your skin care products. Look for and avoid words in the ingredient list like ammonium/sodium/sulfate. The best solution is to use quality cleansers that do not include detergents, such as these: Nature Sustained Raw Dry Skin Body Wash and Hawaii Bubble Shack All-in-One Body Wash