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Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
More than 4.4billion prescriptions were dispensed within the United States in 2016.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.