Symptoms of hair loss include hair loss in patches usually in circular patterns, dandruff, skin lesions, and scarring. Alopecia areata (mild – medium level) usually shows in unusual hair loss areas e.g. eyebrows, backside of the head or above the ears where usually the male pattern baldness does not affect. In male-pattern hair loss, loss and thinning begin at the temples and the crown and either thins out or falls out. Female-pattern hair loss occurs at the frontal and parietal.

People have between 100,000 and 150,000 hairs on their head. The number of strands normally lost in a day varies, but on average is 100. In order to maintain a normal volume, hair must be replaced at the same rate at which it is lost. The first signs of hair thinning that people will often notice are more hairs than usual left in the hairbrush after brushing or in the basin after shampooing. Styling can also reveal areas of thinning, such as a wider parting or a thinning crown.

Baldness is the partial or complete lack of hair growth, and part of the wider topic of "hair thinning". The degree and pattern of baldness varies, but its most common cause is androgenic hair loss, "alopecia androgenetica", or "alopecia seborrheica", with the last term primarily used in Europe.

Classic male-pattern hair loss begins above the temples and vertex (calvaria) of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a 'Hippocratic wreath', and rarely progresses to complete baldness. The Hamilton–Norwood scale has been developed to grade androgenic alopecia in males.

Female-pattern hair loss more often causes diffuse thinning without hairline recession; similar to its male counterpart, female androgenic alopecia rarely leads to total hair loss. The Ludwig scale grades severity of female-pattern hair loss.

Typical first symptoms of alopecia areata are small bald patches. The underlying skin is unscarred and looks superficially normal. Although these patches can take many shapes, they are usually round or oval. Alopecia areata most often affects the scalp and beard, but may occur on any part of the body with hair. Different areas of the skin may exhibit hair loss and regrowth at the same time. The disease may also go into remission for a time, or may be permanent. It is common in children.

The area of hair loss may tingle or be painful. The hair tends to fall out over a short period of time, with the loss commonly occurring more on one side of the scalp than the other.

Exclamation point hairs, narrower along the length of the strand closer to the base, producing a characteristic "exclamation point" appearance, are often present.

When healthy hair is pulled out, at most a few should come out, and ripped hair should not be distributed evenly across the tugged portion of the scalp. In cases of alopecia areata, hair will tend to pull out more easily along the edge of the patch where the follicles are already being attacked by the body's immune system than away from the patch where they are still healthy.

Nails may have pitting or trachyonychia.

The management of hair loss, also known as alopecia or baldness, may include medications and surgery.

Pattern hair loss, known as male-pattern hair loss (MPHL) when it affects males and female-pattern hair loss (FPHL) when it affects females, is hair loss that primarily affects the top and front of the scalp. In males the hair loss often presents as a receding hairline while in females it typically presents as a thinning of the hair.

Male pattern hair loss is believed to be due to a combination of genetics and the male hormone dihydrotestosterone. The cause in female pattern hair loss remains unclear.

Management may include simply accepting the condition. Otherwise, treatments may include minoxidil, finasteride, or hair transplant surgery. Evidence for finasteride in women, however, is poor and it may result in birth defects if taken during pregnancy.

Pattern hair loss by the age of 50 affects about half of males and a quarter of females. It is the most common cause of hair loss.

Hair diseases are disorders primarily associated with the follicles of the hair.

A few examples are

- Alopecia

- Bubble hair deformity

- Hair casts

- Hair loss

- hypertrichosis

- Ingrown hair

- Monilethrix

- Premature greying of hair

- Pattern hair loss

- Trichorrhexis invaginata

Many hair diseases can be associated with distinct underlying disorders.

Piedra are fungal diseases.

Hair disease may refer to excessive shedding or baldness (or both). Balding can be localised or diffuse, scarring or non-scarring. Increased hair can be due to hormonal factors (hirsutism) or non-hormonal (hypertrichosis). Scalp disorders may or may not be associated with hair loss.

In most cases which begin with a small number of patches of hair loss, hair grows back after a few months to a year. In cases with a greater number of patches, hair can either grow back or progress to alopecia areata totalis or, in rare cases, alopecia areata universalis.

There is no loss of body function, and effects of alopecial areata are mainly psychological (loss of self-image due to hair loss), although these can be severe. Loss of hair also means the scalp burns more easily in the sun. Patients may also have aberrant nail formation because keratin forms both hair and nails.

Hair may grow back and then fall out again later. This may not indicate a recurrence of the condition, but rather a natural cycle of growth-and-shedding from a relatively synchronised start; such a pattern will fade over time. Episodes of alopecia areata before puberty predispose to chronic recurrence of the condition.

Alopecia can be the cause of psychological stress. Because hair loss can lead to significant changes in appearance, individuals with it may experience social phobia, anxiety, and depression.

Several lines of evidence support the dermal papilla of the hair follicle as the androgenic target for hair loss prevention and reversal. Type 1 and 2 5α reductase enzymes are present at pilosebaceous units in papillae of individual hair follicles. They catalyse formation of the androgens testosterone and DHT, which in turn regulate hair growth. Androgens have different effects at different follicles: they stimulate IGF-1 at facial hair, causing hair regrowth, but stimulate TGF β1, TGF β2, dickkopf1 and IL-6 at the scalp, causing hair follicle miniaturisation.

Female androgenic alopecia is characterized by diffuse crown thinning without hairline recession, and like its male counterpart rarely leads to total hair loss. Finasteride and minoxidil are usually first line therapy for its treatment. Other options include topical or systemic spironolactone or flutamide, although they have a high incidence of feminising side effects and are better tolerated in female androgenic hair loss.

More advanced cases may be resistant or unresponsive to medical therapy, however, and require hair transplantation. Naturally-occurring units of one to four hairs, called follicular units, are excized and moved to areas of hair restoration. These follicular units are surgically implanted in the scalp in close proximity and in large numbers. The grafts are obtained from either Follicular Unit Transplantation (FUT) – colloquially referred to as "strip harvesting" – or Follicular Unit Extraction (FUE). In the former, a strip of skin with follicular units is extracted and dissected into individual follicular unit grafts. The surgeon then implants the grafts into small incisions, called recipient sites. Specialized scalp tattoos can also mimic the appearance of a short buzzed haircut. Androgenic alopecia also occurs in women, and more often presents as diffuse thinning without hairline recession. Like its male counterpart, the condition rarely leads to total hair loss. Treatment options are similar to those for men, although topical or systemic estrogen is used more often.

Hypotrichosis ("" + "" + "") is a condition of abnormal hair patterns, predominantly loss or reduction. It occurs, most frequently, by the growth of vellus hair in areas of the body that normally produce terminal hair. Typically, the individual's hair growth is normal after birth, but shortly thereafter the hair is shed and replaced with sparse, abnormal hair growth. The new hair is typically fine, short and brittle, and may lack pigmentation. Baldness may be present by the time the subject is 25 years old.

Hypotrichosis is a common feature of Hallermann–Streiff syndrome as well as others. It can also be used to describe the lack of hair growth due to chemotherapy.

The opposite of hypotrichosis is hypertrichosis, where terminal hair (thick) grows in areas that would otherwise normally have vellus hair (thin), for example abnormally thick facial hair growth in women.

The presentation may be of alopecia (baldness). Individuals vary in severity of symptoms. Nail deformities may also be present as well as hair follicle keratosis and follicular hyperkeratosis.

Genetic forms of localized autosomal recessive hypotrichosis include:

Monilethrix (also referred to as beaded hair) is a rare autosomal dominant hair disease that results in short, fragile, broken hair that appears beaded. It comes from the Latin word for necklace ("monile") and the Greek word for hair ("thrix").

Actinic keratoses ("AKs") most commonly present as a white, scaly plaque of variable thickness with surrounding redness; they are most notable for having a sandpaper-like texture when felt with a gloved hand. Skin nearby the lesion often shows evidence of solar damage characterized by notable pigmentary alterations, being yellow or pale in color with areas of hyperpigmentation; deep wrinkles, coarse texture, purpura and ecchymoses, dry skin, and scattered telangiectasias are also characteristic. Photoaging leads to an accumulation of oncogenic changes, resulting in a proliferation of mutated keratinocytes that can manifest as AKs or other neoplastic growths. With years of sun damage, it is possible to develop multiple AKs in a single area on the skin.

The lesions are usually asymptomatic, but can be tender, itch, bleed, or produce a stinging or burning sensation. AKs are typically graded in accordance with their clinical presentation: Grade I (easily visible, slightly palpable), Grade II (easily visible, palpable), and Grade III (frankly visible and hyperkeratotic).

Actinic keratoses can have various clinical presentations, often characterized as follows:

- Classic (or common): Classic AKs present as white, scaly macules, papules or plaques of various thickness, often with surrounding erythema. They are usually 2-6mm in diameter but can sometimes reach several centimeters in diameter.

- Hypertrophic (or hyperkeratotic): Hypertrophic AKs (HAKs) appear as a thicker scale or rough papule or plaque, often adherent to an erythematous base. Classic AKs can progress to become HAKs, and HAKs themselves can be difficult to distinguish from malignant lesions.

- Atrophic: Atrophic AKs lack an overlying scale, and therefore appear as a nonpalpable change in color (or macule). They are often smooth and red, and are less than 10mm in diameter.

- AK with cutaneous horn: A cutaneous horn is a keratinic projection with its height at least one-half of its diameter, often conical in shape. They can be seen in the setting of actinic keratosis as a progression of an HAK, but are also present in other skin conditions. 38–40% of cutaneous horns represent AKs.

- Pigmented AK: Pigmented AKs are rare variants that often present as macules or plaques that are tan to brown in color. They can be difficult to distinguish from a solar lentigo or lentigo maligna.

- Actinic cheilitis: When an AK forms on the lip, it is called actinic cheilitis. This usually presents as a rough, scaly patch on the lip, often accompanied by the sensation of dry mouth and symptomatic splitting of the lips.

- Bowenoid AK: Usually presents as a solitary, erythematous, scaly patch or plaque with well-defined borders. Bowenoid AKs are differentiated from Bowen's disease by degree of epithelial involvement as seen on histology.

The presence of ulceration, nodularity, or bleeding should raise concern for malignancy. Specifically, clinical findings suggesting an increased risk of progression to squamous cell carcinoma can be recognized as "IDRBEU": I (induration /inflammation), D (diameter > 1 cm), R (rapid enlargement), B (bleeding), E (erythema) and U (ulceration). AKs are usually diagnosed clinically, but because they are difficult to clinically differentiate from squamous cell carcinoma, any concerning features warrant biopsy for diagnostic confirmation.

Areas affected are those the cat can access most easily, including the abdomen, legs, flank, and chest.

- Baldness, usually beginning with the abdomen

- Obvious over-grooming (although some cats may only engage in the behavior in the absence of owners)

- Redness, rashes, pus, scabs on the bald area or areas traumatized by over-grooming

- A highly irritable cat may even cut its face with the claw of its hind foot if over-zealously scratching the back of its head.

Individuals with 5-ARD are born with male gonads, including testicles and Wolffian structures. They can have normal male external genitalia, ambiguous genitalia, or normal female genitalia, but usually tend towards a female appearance. As a consequence, they are often raised as girls, but usually have a male gender identity.

The development of the genital tubercle tissue (which by week 9 of a fetus' gestation becomes either a clitoris or a penis) tends towards a size qualifying it as an ambiguous macroclitoris/micropenis (large clitoris/small penis), and the urethra may attach to the phallus.

If the condition has not already been diagnosed, it usually becomes apparent at puberty around age twelve with primary amenorrhoea and virilization. This may include descending of the testes, hirsutism (facial/body hair considered normal in males - not to be confused with hypertrichosis), deepening of the voice, and enlargement of the clitoris into what would then be classed as a penis.

In adulthood, individuals do not experience male-pattern baldness. As DHT is a far more potent androgen than testosterone alone, virilization in those lacking DHT may be absent or reduced compared to males with functional 5-AR. It is hypothesized that rising testosterone levels at the start of puberty are able to generate sufficient levels of DHT either by the action of 5α-reductase type I (active in the adult liver, non-genital skin and some brain areas) or through the expression of low levels of 5α-reductase type II in the testes.

5-ARD is associated with an increased risk of cryptorchidism and testicular cancer.

Severe prenatal deficiency of GH, as occurs in congenital hypopituitarism, has little effect on fetal growth. However, prenatal and congenital deficiency can reduce the size of a male's penis, especially when gonadotropins are also deficient. Besides micropenis in males, additional consequences of severe deficiency in the first days of life can include hypoglycemia and exaggerated jaundice (both direct and indirect hyperbilirubinemia).

Even congenital GH deficiency does not usually impair length growth until after the first few months of life. From late in the first year until mid teens, poor growth and/or shortness is the hallmark of childhood GH deficiency. Growth is not as severely affected in GH deficiency as in untreated hypothyroidism, but growth at about half the usual velocity for age is typical. It tends to be accompanied by delayed physical maturation so that bone maturation and puberty may be several years delayed. When severe GH deficiency is present from birth and never treated, adult heights can be as short as 48-65 inches (122–165 cm).

Severe GH deficiency in early childhood also results in slower muscular development, so that gross motor milestones such as standing, walking, and jumping may be delayed. Body composition (i.e., the relative amounts of bone, muscle, and fat) is affected in many children with severe deficiency, so that mild to moderate chubbiness is common (though GH deficiency alone rarely causes severe obesity). Some severely GH-deficient children have recognizable, cherubic facial features characterized by maxillary hypoplasia and forehead prominence (said to resemble a kewpie doll).

Other side effects in children include sparse hair growth and frontal recession, and pili torti and trichorrhexis nodosa are also sometimes present.

Growth hormone deficiency can be congenital or acquired in childhood or adult life. It can be partial or complete. It is usually permanent, but sometimes transient. It may be an isolated deficiency or occur in association with deficiencies of other pituitary hormones.

The term hypopituitarism is often used interchangeably with GH deficiency but more often denotes GH deficiency plus deficiency of at least one other anterior pituitary hormone. When GH deficiency (usually with other anterior pituitary deficiencies) is associated with posterior pituitary hormone deficiency (usually diabetes insipidus), the condition is termed panhypopituitarism.

Psychogenic alopecia, also called "over-grooming" or "psychological baldness," is a compulsive behavior that affects domestic cats. Generally, psychogenic alopecia does not lead to serious health consequences or a decreased lifespan.

Although the external genitalia can sometimes be completely female, the vagina consists of only the lower two-thirds of a normal vagina, creating a blind-ending vaginal pouch.

Since the gonad tissue develops into testes rather than ovaries, they are thus unable to create ova but may be able to create sperm. Because of normal action of Müllerian inhibiting factor produced by the testes in utero, individuals with 5-ARD lack a uterus and Fallopian tubes. Thus, they would not physically be able to carry a pregnancy in any event. Even with treatments such as surrogate motherhood, female infertility is caused by the lack of any ova to implant in a surrogate. Male fertility, however, can still be possible if viable sperm is present in the testes and is able to be extracted. In general, individuals with 5-ARD are capable of producing viable sperm.

In individuals with an ambiguous genital resulting in a macroclitoris/micropenis, the genital may be capable of ejaculations as well as erections, but may be of insufficient size for penetrative sexual intercourse.

Fertility is further compromised by the underdevelopment of seminal vesicles and prostate.

Hair is one of the defining characteristics of mammals. In humans, hair can be scalp hair, facial hair, chest hair, pubic hair, axillary hair, besides other places. Men tend to have hair in more places than women. Hair does not in itself have any intrinsic sexual value other than the attributes given to it by individuals in a cultural context. Some cultures are ambivalent in relation to body hair, with some being regarded as attractive while others being regarded as unaesthetic. Many cultures regard a woman's hair to be erotic. For example, many Islamic women cover their hair in public, and display it only to their family and close friends. Similarly, many Jewish women cover their hair after marriage. During the Middle Ages, European women were expected to cover their hair after they married.

Even in cultures where women do not customarily cover their hair, the erotic significance of hair is recognised. Some hair styles are culturally associated with a particular gender, with short head hair styles and baldness being associated with men and longer hair styles with women and girls, even though there are many exceptions such as Gaelic Irish men, and also depictions of men in art throughout history, the most notable example probably being that of Jesus Christ. In the case of women especially, head hair has been presented in art and literature as a feature of beauty, vanity and eroticism. Hair has a very important role in the canons of beauty in different regions of the world, and healthy combed hair has two important functions, beauty and fashion. In those cultures considerable time and expense is put into the attractive presentation of hair, and in some cases to the removal of culturally unwanted hair.

Hair fetishism manifests itself in a variety of behaviors. A fetishist may enjoy seeing or touching hair, pulling on or cutting the hair of another person. Besides enjoyment they may become sexually aroused from such activities. It may also be described as an obsession, as in the case of hair washing or dread of losing hair. Arousal by head hair may arise from seeing or touching very long or short hair, wet hair, a certain color of hair or a particular hairstyle. Others may find the attraction of literally "having sex with somebody's hair" as a fantasy or fetish. The fetish affects both men and women.

Some people feel pleasure when their hair is being cut or groomed. This is because they produce endorphins giving them a feeling which is similar to that of a head massage, laughter, or caress. On the other hand, many people feel some level of anxiety when their head hair is being cut. Sigmund Freud stated that cutting woman's long hair by men may represent a fear and/or concept of castration, meaning that a woman's long hair represents a figurative penis and that by cutting off her hair a man may feel dominance as castrator, not the castrated one (while paradoxically also being reassured by the fact that the hair will grow again).

Trichophilia may present with different excitation sources, the most common, but not the only one, being human head hair. Trichophilia may also involve facial hair, chest hair, pubic hair, armpit hair and animal fur. The excitation can arise from the texture, color, hairstyle and hair length. Among the most common variants of this paraphilia are excitation by long hair and short hair, the excitement of blonde hair (blonde fetishism) and red hair (redhead fetishism) and the excitement of the different textures of hair (straight, curly, wavy, etc.). Trichophilia can relate to the excitement that is caused by plucking or pulling hair or body hair.

Hair fetishism comes from a natural fascination with the species on the admiration of the coat, as its texture provides pleasurable sensations. An infant develops this kind of pleasure to feel the hair on his or her early life, manifesting as aggressive behavior that will drive to pull the hair of people with which it interacts. Trichophilia is considered a paraphilia which is usually inoffensive.

Hair fetishism, also known as hair partialism and trichophilia, is a partialism in which a person sees hair most commonly, head hair as particularly erotic and sexually arousing. Arousal may occur from seeing or touching hair, whether head hair, pubic hair, axillary hair, chest hair or fur. Head-hair arousal may come from seeing or touching very long or short hair, wet hair, certain colors of hair or a particular hairstyle. Pubic hair fetishism is a particular form of hair fetishism.

Haircut fetishism is a related paraphilia in which a person is aroused by having their head hair cut or shaved, by cutting the hair of another, by watching someone get a haircut, or by seeing someone with a shaved head or very short hair.

Common signs and symptoms of PCOS include the following:

- Menstrual disorders: PCOS mostly produces oligomenorrhea (fewer than nine menstrual periods in a year) or amenorrhea (no menstrual periods for three or more consecutive months), but other types of menstrual disorders may also occur.

- Infertility: This generally results directly from chronic anovulation (lack of ovulation).

- High levels of masculinizing hormones: Known as hyperandrogenism, the most common signs are acne and hirsutism (male pattern of hair growth, such as on the chin or chest), but it may produce hypermenorrhea (heavy and prolonged menstrual periods), androgenic alopecia (increased hair thinning or diffuse hair loss), or other symptoms. Approximately three-quarters of women with PCOS (by the diagnostic criteria of NIH/NICHD 1990) have evidence of hyperandrogenemia.

- Metabolic syndrome: This appears as a tendency towards central obesity and other symptoms associated with insulin resistance. Serum insulin, insulin resistance, and homocysteine levels are higher in women with PCOS.

Asians affected by PCOS are less likely to develop hirsutism than those of other ethnic backgrounds.

Typically guttate psoriasis erupts after a throat infection, or strep throat. Initially, when the throat infection has cleared up, the person can feel fine for several weeks before noticing the appearance of red spots. They appear small at first, like a dry red spot which is slightly itchy. When scratched or picked the top layer of dry skin is removed, leaving dry, red skin beneath with white, dry areas marking where flakes of dry skin stop and start. In the weeks that follow the spots can grow to as much as an inch in diameter. Some of the larger ones may form a pale area in the center which is slightly yellow.

Guttate psoriasis can occur on any part of the body, particularly the legs, arms, torso, eyelids, back, bottom, bikini-line and neck. The number of lesions can range from 5 to over 100. Generally the parts of the body most affected are seen on the arms, legs, back and torso.