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About 600,000 particles of skin are shed every hour by each human. If you live to age 70 years, you have shed 105 pounds of dead skin.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
Asthma is the most common chronic childhood disease in the world. Most children who develop asthma have symptoms before they are 5 years old.