This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Chest hair" – news · newspapers · books · scholar · JSTOR (April 2020) (Learn how and when to remove this message) This article is written like a personal reflection, personal essay, or argumentative essay that states a Wikipedia editor's personal feelings or presents an original argument about a topic. Please help improve it by rewriting it in an encyclopedic style. (April 2020) (Learn how and when to remove this message) (Learn how and when to remove this message)

Chest hair is hair that grows on the chest in the region between the neck and the abdomen. Chest hair develops during and after puberty along with other types of androgenic hair.

Although vellus hair is already present in the area in childhood, chest hair is 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. Men tend to be covered with far more terminal hair, particularly on the chest, the abdomen, and the face.

The development of chest hair begins normally during late puberty, usually between the ages of 12 and 18. 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.

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. All ranges and patterns of hair growth are 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 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.^{[citation needed]}

Considering an individual occurrence of chest hair as abnormal is usually not due to medical indications but primarily to cultural and social attitudes. An excessive growth of terminal hair on the body 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 1,400 white men aged 17 to 71 conducted by L.R. Setty in the 1960s defines 15 patterns of chest hair.^[1][2][3][4] In this study, four parts of the chest in which terminal hair occurs were identified:

Chest hair may occur on each of these areas independent from the others, making for a total of 15 combinations in addition to the apilose (bare) pattern. Hair is said to occur on both the pectoral and circumareolar areas when there is hair around the nipples and on the breast, but these areas are not connected.

A	C	CI	CS
CP	CPI	CPS	CPSI
CSI	I	P	PI
PS	PSI	S	SI
The 16 chest hair patterns by Setty

The pecto-sterno-infraclavicular pattern, in which the breast, sternum and medial end of the clavicle is covered with terminal hair, is most common (57%).

• 
  CS – Chest hair primarily on sternum and around the nipples
• 
  PS – Chest hair on sternum and breast
• 
  PSI – Hair on sternum, breast and medial end of clavicle

• Abdominal hair
• Hair

Wikimedia Commons has media related to Chest hair.

• Setty, LR (1961). "Bare areas in regions of pilosity of the chest and abdomen". Journal of the National Medical Association. 53 (4): 394–5. PMC 2641808. PMID 13750402.
• Lookingbill, DP; Demers, LM; Wang, C; Leung, A; Rittmaster, RS; Santen, RJ (1991). "Clinical and biochemical parameters of androgen action in normal healthy Caucasian versus Chinese subjects". The Journal of Clinical Endocrinology and Metabolism. 72 (6): 1242–8. doi:10.1210/jcem-72-6-1242. PMID 1827450.