Chest hair
The term chest hair is generally used to describe hair that grows on the chest of human males, in the region between the neck and the abdomen. Chest hair, which is a secondary sex characteristic, develops during and after puberty. It is therefore part of the androgenic hair.

# Development and growth
Although vellus hair is already present in the area in childhood, the term chest hair is generally restricted to the terminal hair that develops as an effect of rising levels of androgens (primarily testosterone and its derivatives) due to puberty. Different from the head hair it is therefore a secondary sexual characteristic. In contrast to women the body of men tends to be covered far more with terminal hair, particularly on the chest, the abdomen and the face.
The development of chest hair begins normally during late puberty. It can also start later, between the age of 20 and 30, so that many men in their twenties have not yet reached their full chest hair development. The growth continues subsequently. In older adult years androgens cause thickening of the hair.

# Patterns and characteristics
The individual occurrence and characteristics of chest hair depend on the genetic disposition, the hormonal status and the age of the person. The genes primarily determine the amount, patterns and thickness of chest hair. Some men are very hairy, while others have no chest hair at all. Each pattern of hair growth is normal. The areas where terminal hair may grow are the periareolar areas (nipples), the centre and sides of the chest and the clavicle (collarbone).
The direction of growth of hair can make for interesting patterns, akin to depictions of mathematical vector fields.  Typical males will exhibit
a node on the upper sternum, the hair above which points up and the hair below which points down.  Some individuals (of say the pattern in diagram 3) have spirals on their upper pectoral regions (several inches from the nipple towards the neck) which run clockwise on the left breast and counter-clockwise on the right.
Considering an individual occurrence of chest hair as abnormal does not implicitly depend on medical indications but primarily on cultural and social attitudes. An excessive growth of terminal hair on the body of men and women is called hypertrichosis. This medical term has to be distinguished from hirsutism that just affects women. These women can develop terminal hair on the chest following the male pattern as a symptom of an endocrine disease.
There have been occasional studies documenting patterns of chest hair in men and occurrence of these patterns. A study of 1100 men aged 17 to 71 defined and documented ten patterns of chest hair in Caucasoid men. In this study 6 percent of the men were found to have no chest hair. The largest group, 56 percent, displayed pattern four as shown in the accompanying figure. The remaining 38 percent of the men displayed a lesser quantity of chest hair. Seven percent displayed pattern one, 13 percent displayed pattern two and 18 percent displayed various other patterns.
The same study documented the chest hair patterns of 60 African-American men aged 20-40. For these men 22 percent were found to have no chest hair. The largest group, 37 percent displayed pattern four and the remaining 41 percent had a lesser quantity of chest hair. Eight percent displayed pattern one, 12 percent pattern two and 11 percent displayed various other patterns. 

# Cultural and social attitudes
The attitudes towards chest hair vary between different cultures and times. In some cultures, it is a symbol for virility and masculinity; other societies display a hairless body as a sign of youthfulness. Some people find men with a lot of chest hair, pattern four, very sexually arousing. In ancient Greece and ancient Rome male statues did not show any chest hair. Even on paintings and sculptures from Middle Ages to modern times men were often portrayed without any hair on their anterior torso.
While in the early and middle twentieth century the attitude towards hair on the chest was largely indifferent, there was a late twentieth century trend within Western societies to remove chest hair. Some young men in their teens and twenties, especially in the United States and those involved in beach culture, remove their chest hair. It is quite common for actors, who will appear shirtless in a movie or television show, to shave their chests. The removal of body hair (depilation and epilation) by men was labelled by the personal hygiene industry as manscaping. This public trend, distributed by the media, began in the United States and spread to other Western societies. Many companies catered to men looking for ways to remove their chest hair, such as Nair for Men and Nads for Men. While most men depicted in fashion advertising still have no chest hair, a few exceptions can now be seen. Bucking the larger trend, a positive acceptance of body hair could be found amongst adherents of naturism as well as the bear community, the latter a gay subculture whose members tend to exhibit typical masculine gender traits.  Removing or maintaining chest hair ultimately depends on one's individual preference, which can be influenced by what is considered most attractive.