Head and Shoulders Dandruff Conditioner, Dry Scalp Care, 21.9 fl oz

Twenty-one, XXI or 21 may refer to:

• 21 (number), the natural number following 20 and preceding 22
• One of the years 21 BC, AD 21, 1921, 2021

A conditioner is something that improves the quality of another item.

Conditioner may refer to:

• Conditioner (chemistry)
• Conditioner (farming)
• Air conditioner
• Fabric conditioner
• Hair conditioner
• Leather conditioner
• Power conditioner
• The apparatus that contains most of the resurfacing components on an ice resurfacer

Dandruff is a skin condition that mainly affects the scalp. Symptoms include flaking and sometimes mild itchiness. It can result in social or self-esteem problems. A more severe form of the condition, which includes inflammation of the skin, is known as seborrhoeic dermatitis.

The cause is unclear, but believed to involve a number of genetic and environmental factors; the condition may worsen in the winter. It is not due to poor hygiene, and the underlying mechanism involves the excessive growth of skin cells. Diagnosis is based on symptoms.

There is no known cure for dandruff. Antifungal cream, such as ketoconazole, or the keratolytic agent salicylic acid may be used to try to improve the condition. Dandruff affects about half of adults, with males more often affected than females. In addition, people in all areas of the world are affected. Onset is usually at puberty, and it becomes less common after the age of 50.

Dry or dryness most often refers to:

• Lack of rainfall, which may refer to
  • Arid regions
  • Drought
• Dry or dry area, relating to legal prohibition of selling, serving, or imbibing alcoholic beverages
• Dry humor, deadpan
• Dryness (medical)
• Dryness (taste), the lack of sugar in a drink, especially an alcoholic one
• Dry direct sound without reverberation

Dry or DRY may also refer to:

A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may not have a head, but many bilaterally symmetric forms do, regardless of size.

Heads develop in animals by an evolutionary trend known as cephalization. In bilaterally symmetrical animals, nervous tissue concentrate at the anterior region, forming structures responsible for information processing. Through biological evolution, sense organs and feeding structures also concentrate into the anterior region; these collectively form the head.

The scalp is the area of the head where head hair grows. It is made up of skin, layers of connective and fibrous tissues, and the membrane of the skull. Anatomically, the scalp is part of the epicranium, a collection of structures covering the cranium. The scalp is bordered by the face at the front, and by the neck at the sides and back. The scientific study of hair and scalp is called trichology.