As comets move close to the Sun, they develop tails of dust and ionized gas. Comets have two main tails, a dust tail and a plasma tail. The dust tail appears whitish-yellow because it is made up of tiny particles â about the size of particles of smoke â that reflect sunlight. Dust tails are typically between 1 and 10 million kilometers (about 600,000 to 6 million miles) long.
Hyperhidrosis, or excessive sweating, is a common disorder which produces a lot of unhappiness. An estimated 2-3% of Americans suffer from excessive sweating of the underarms (axillary hyperhidrosis) or of the palms and soles of the feet (palmoplantar hyperhidrosis). Underarm problems tend to start in late adolescence, while palm and sole sweating often begins earlier, around the age 13 (on the average). Untreated, these problems may continue throughout life. Sweating is embarrassing, it stains clothes, ruins romance, and complicates business and social interactions.
Excessive sweating can be normal, if it is caused by factors like high atmospheric temperature. For some people, sweating could be almost persistent and profuse. This condition (excessive sweating) is called hyperhidrosis. It may affect the whole body or specific body parts like soles of feet, palms and head. Excessive head sweating is called cranial hyperhidrosis. As in case of other types (of hyperhidrosis), cranial hyperhidrosis can also be primary or secondary. The condition is categorized as primary cranial hyperhidrosis, if it is a disease in itself and is not caused by any other underlying medical condition.