Chest hairishair 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.
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.
Four areas in the Setty chest hair pattern system: infraclavicular (top), pectoral (left), sternal (middle) and circumareolar (right)
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:
The breast area, including the area immediately around the areola (nipples);
77%
Circumareolar
A small area immediately encircling the areola.
16%
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.
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%).
^Setty, LR (1961). "The Distribution of Chest Hair in Caucasoid Males". American Journal of Physical Anthropology. 19 (3): 285–7. doi:10.1002/ajpa.1330190309. PMID13910982.
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. PMID1827450.
