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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.
Asthma occurs in one in 11 children and in one in 12 adults. African Americans and Latinos have a higher risk for developing asthma than other groups.
More than 20 million Americans cite use of marijuana within the past 30 days, according to the National Survey on Drug Use and Health (NSDUH). More than 8 million admit to using it almost every day.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.