The Eustachian tube is used to equalize air pressure between the middle ear and the surrounding area, but it is also used to drain mucus from the middle ear. Keeping the pressure in a person's head equalized helps with balance and preventing dizziness.
Mutations can also be caused by environmental foes. Tobacco, ultraviolet light and other chemicals are all potential enemies of DNA. One way these hazards attack our genes is very sneaky: They have the ability to damage the chemicals making up DNA.
The photoproducts interfere with DNA replication if not repaired and cause specific mutations in DNA. The specific mutations induced by UV-B in DNA sequences most often include single-base substitutions of cytosine (C) for thymine (T).