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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:
| Area | Description | Incidence [2] |
|---|---|---|
| Sternal | The center and lower part of the body of the breastbone | 74% |
| Infraclavicular | The area immediately below the medial end of the collarbone; | 63% |
| Pectoral | 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.
 A |  C |  CI |  CS |
 CP |  CPI |  CPS |  CPSI |
 CSI |  I |  P |  PI |
 PS |  PSI |  S |  SI |
| The 16 chest hair patterns by Setty | |||
| Pattern | Name | Incidence [2] |
|---|---|---|
| A | Apilose | 6% |
| C | Circumareolar | 6% |
| CI | Circumareolo-infraclavicular | 1.5% |
| CP | Circumareolo-pectoral | 0.1% |
| CPI | Circumareolo-pecto-infraclavicular | 0.1% |
| CPS | Circumareolo-pecto-sternal | 0.1% |
| CPSI | Circumareolo-pecto-sterno-infraclavicular | 0.1% |
| CS | Circumareolo-sternal | 5% |
| CSI | Circumareolo-sterno-infraclavicular | 2% |
| I | Infraclavicular | 0.5% |
| P | Pectoral | 5% |
| PI | Pecto-infraclavicular | 1.5% |
| PS | Pecto-sternal | 13% |
| PSI | Pecto-sterno-infraclavicular | 57% |
| S | Sternal | 1.7% |
| SI | Sterno-infraclavicular | 0.1% |
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%).
The breasts are two prominences located on the upper ventral region of the torso among humans and other primates. Both sexes develop breasts from the same embryological tissues. The relative size and development of the breasts is a major secondary sex distinction between females and males. There is also considerable variation in size between individuals. Female humans are the only mammals which permanently develop breasts at puberty; all other mammals develop their mammary tissue during the latter period of pregnancy; at puberty, estrogens, in conjunction with growth hormone, cause permanent breast growth.
Pubic hair is terminal body hair that is found in the genital area and pubic region of adolescent and adult humans. The hair is located on and around the sex organs, and sometimes at the top of the inside of the thighs, even extending down the perineum, and to the anal region. Pubic hair is also found on the scrotum and base of the penile shaft and on the vulva. Around the pubis bone and the mons pubis that covers it, it is known as a pubic patch, which can be styled.
The thorax or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen.
Reduction mammoplasty is the plastic surgery procedure for reducing the size of large breasts. In a breast reduction surgery for re-establishing a functional bust that is proportionate to the patient's body, the critical corrective consideration is the tissue viability of the nipple–areola complex (NAC), to ensure the functional sensitivity and lactational capability of the breasts. The indications for breast reduction surgery are three-fold – physical, aesthetic, and psychological – the restoration of the bust, of the patient's self-image, and of the patient's mental health.
The pectoralis major is a thick, fan-shaped or triangular convergent muscle of the human chest. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor muscle.
Pubarche refers to the first appearance of pubic hair at puberty. It is one of the physical changes of puberty and can occur independently of complete puberty. The early stage of sexual maturation, also known as adrenarche, is marked by characteristics including the development of pubic hair, axillary hair, adult apocrine body odor, acne, and increased oiliness of hair and skin. The Encyclopedia of Child and Adolescent Health corresponds SMR2 with pubarche, defining it as the development of pubic hair that occurs at a mean age of 11.6 years in females and 12.6 years in males. It further describes that pubarche's physical manifestation is vellus hair over the labia or the base of the penis. See Table 1 for the entirety of the sexual maturity rating description.
The axilla is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superiorly by the imaginary plane between the superior borders of the first rib, clavicle and scapula, medially by the serratus anterior muscle and thoracolumbar fascia, anteriorly by the pectoral muscles and posteriorly by the subscapularis, teres major and latissimus dorsi muscle.
Vellus hair is short, thin, light-colored, and barely noticeable hair that develops on most of a human's body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital areas, the navel, and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm long and the follicle is not connected to a sebaceous gland.
The intermammary cleft, intermammary sulcus, or sulcus intermammarius is a surface feature of males and females that marks the division of the two breasts with the sternum (breastbone) in the middle. The International Federation of Associations of Anatomists (IFAA) uses the terms "sulcus intermammarius" or "intermammary cleft" when referring to the area between the breasts.
Poland syndrome is a birth defect characterized by an underdeveloped chest muscle and short webbed fingers on one side of the body. There may also be short ribs, less fat, and breast and nipple abnormalities on the same side of the body. Typically, the right side is involved. Those affected generally have normal movement and health.
Abdominal hair is the hair that grows on the abdomen of humans and non-human mammals, in the region between the pubic area and the thorax (chest). The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax downwards to the navel. The abdominal hair of non-human mammals is part of the pelage,.
Body hair or androgenic hair is terminal hair that develops on the human body during and after puberty. It is different from head hair and also from less visible vellus hair, which is much finer and lighter in color. Growth of androgenic hair is related to the level of androgens and the density of androgen receptors in the dermal papillae. Both must reach a threshold for the proliferation of hair follicle cells.
Mastopexy is the plastic surgery mammoplasty procedure for raising sagging breasts upon the chest of the woman, by changing and modifying the size, contour, and elevation of the breasts. In a breast-lift surgery to re-establish an aesthetically proportionate bust for the woman, the critical corrective consideration is the tissue viability of the nipple-areola complex (NAC), to ensure the functional sensitivity of the breasts for lactation and breast-feeding.
Masculinizing hormone therapy, also known as transmasculine hormone therapy or female-to-male hormone therapy, is a form of hormone therapy and gender affirming therapy which is used to change the secondary sexual characteristics of transgender people from feminine or androgynous to masculine. It is a common type of transgender hormone therapy, and is predominantly used to treat transgender men and other transmasculine individuals who were assigned female at birth. Some intersex people also receive this form of therapy, either starting in childhood to confirm the assigned sex or later if the assignment proves to be incorrect.
Feminizing hormone therapy, also known as transfeminine hormone therapy, is hormone therapy and sex reassignment therapy to change the secondary sex characteristics of transgender people from masculine or androgynous to feminine. It is a common type of transgender hormone therapy and is used to treat transgender women and non-binary transfeminine individuals. Some, in particular intersex people, but also some non-transgender people, take this form of therapy according to their personal needs and preferences.
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a female, the testicles in a male. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed. Before puberty, the external sex organs, known as primary sexual characteristics, are sex characteristics that distinguish males and females. Puberty leads to sexual dimorphism through the development of the secondary sex characteristics, which further distinguish the sexes.
Supernumerary nipples–uropathies–Becker's nevus syndrome is a skin condition that may be associated with genitourinary tract abnormalities. Supernumerary nipples, also referred to as polythelia or accessory nipples, is a pigmented lesion of the skin that is present at birth. This pigmentation usually occurs along the milk lines, which are the precursors to breast and nipple development. Clinically, this congenital condition is generally considered benign, but some studies have suggested there may be an association with kidney diseases and cancers of the urogenital system.
Prepubertal hypertrichosis, also known as childhood hypertrichosis, is a cutaneous condition characterized by increased hair growth, found in otherwise healthy infants and children. Prepubertal hypertrichosis is a cosmetic condition and does not affect any other health aspect. Individuals with this condition may suffer with low self esteem and mental health issues due to societal perceptions of what a "normal" appearance should be. The mechanism of prepubertal hypertrichosis is unclear, but causes may include genetics, systemic illnesses, or medications.
The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Shaped roughly like a necktie, it is one of the largest and longest flat bones of the body. Its three regions are the manubrium, the body, and the xiphoid process. The word sternum originates from Ancient Greek στέρνον (stérnon) 'chest'.
Gynecomastia is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Gynecomastia can cause significant psychological distress or unease.
