Melasma is thought to be the stimulation of melanocytes (cells in the epidermal layer of skin that produce a pigment called melanin) by the female sex hormones estrogen and progesterone to produce more melanin pigments when the skin is exposed to sun. Women with a light brown skin type who are living in regions with intense sun exposure are particularly susceptible to developing this condition.

Genetic predisposition is also a major factor in determining whether someone will develop melasma.

The incidence of melasma also increases in patients with thyroid disease. It is thought that the overproduction of melanocyte-stimulating hormone (MSH) brought on by stress can cause outbreaks of this condition. Other rare causes of melasma include allergic reaction to medications and cosmetics.

Melasma Suprarenale "(Latin - above the kidneys)" is a symptom of Addison's disease, particularly when caused by pressure or minor injury to the skin, as discovered by Dr. FJJ Schmidt of Rotterdam in 1859.

Razor burn is a less serious condition caused by shaving, characterized by mild to moderate redness and irritation on the surface of the skin. Unlike PFB, it is usually transient and there is no infection involved.

There is also a condition called "folliculitis barbae". The difference between the two is the cause of the inflammation in the hair follicles. Folliculitis barbae is caused by viral or bacterial infections, where pseudofolliculitis is caused by irritation from shaving and ingrown hairs.

A related condition, pseudofolliculitis nuchae, occurs on the back of the neck, often along the posterior hairline, when curved hairs are cut short and allowed to grow back into the skin. Left untreated, this can develop into acne keloidalis nuchae, a condition where hard, dark keloid-like bumps form on the neck. Both occur frequently in black men in the military, where it is so common that services often have widely known protocols for management

The lack of nutrients in the diet, or the lack of a balanced diet, can contribute to the discoloration of the area under the eyes. It is believed that iron deficiency can cause dark circles as well. Iron deficiency is the most common type of anemia and this condition is a sign that not enough oxygen is getting to the body tissues.

The skin can also become more pale during pregnancy and menstruation (due to lack of iron), allowing the underlying veins under the eyes to become more visible.

This condition is self-limiting. Improvements in grooming techniques and in environmental conditions will correct the abnormality.

Avoid aggressive brushing and grooming, strong chemicals, permanents, straightening, and similar hair-damaging habits.

Schamberg's disease is caused by leaky blood vessels near the surface of the skin, capillaries, which allow red blood cells to slip through into the skin. The red blood cells in the skin then fall apart and release their iron, which is released from hemoglobin. The iron causes a rust color and this accounts for the orange tint of the rash that can be seen on the skin. The underlying cause of the leaky blood vessels is not known, but researchers are suggesting that there could be some potential triggers. Some possible triggers include viral infection, a hypersensitivity to some agent, and interaction of some medications, such as thiamine and aspirin. Even though there is no correlation with genetics, there have been a few cases where few people in a family had this condition.

Although the cause of capillary inflammation is unknown, certain preventive measures can be taken. Doctors may prescribe medications that enhance the circulation of blood, which can keep blood vessels strong and healthy. Daily intake of vitamin C has proven to be a natural home remedy that can prevent the onsite of any disease or infection. Doctors always recommend that their patients monitor what they eat because their diet could be a possible factor that contributes to this condition. A healthy body that receives nutritious meals is more likely to have a healthy life that does not revolve around a lot of health problems.

Any medications that cause blood vessels to dilate can cause circles under the eyes to darken. Because the skin under the eyes is very delicate, any increased blood flow shows through the skin.

AC is caused by chronic and excessive exposure to ultraviolet radiation in sunlight.

Risk factors include:

- Outdoor lifestyle: e.g. farmers, sailors, fishermen, windsurfers, mountaineers, golfers, etc. This has given rise to synonyms for this condition such as "sailor's lip" and "farmer's lip". The prevalence in agricultural workers in a semi-arid region of Brazil is reported to be 16.7%.

- Light skin complexion: the condition typically affects individuals with lighter skin tones, particularly Caucasians living in tropical regions. In one report, 96% of persons with AC had phenotype II according to the Fitzpatrick scale.

- Age: AC typically affects older individuals, and rarely those under the age of 45.

- Gender: the condition affects males more commonly than females. Sometimes this ratio is reported as high as 10:1.

Additional factors may also play a role, including tobacco use, lip irritation, poor oral hygiene, and ill-fitting dentures.

Melasma is usually diagnosed visually or with assistance of a Wood's lamp (340 - 400 nm wavelength). Under Wood's lamp, excess melanin in the epidermis can be distinguished from that of the dermis.

Many other conditions can lead to localized scaling or hyperpigmentation.

This condition should firmly be distinguished from dermatitis artefacta, which is the "factitious" creation of a skin lesion, whereas dermatosis neglecta results from unconscious avoidance of cleaning due to pain or immobility.

Other skin conditions which should not be mistaken for dermatosis neglecta include: terra firma-forme dermatosis (in which there is no history of inadequate cleaning); confluent and reticulated papillomatosis of Gougerot and Carteaud; several forms of ichthyosis; acanthosis nigricans; and Vagabond's disease.

To prevent AC from developing, protective measures could be undertaken such as avoiding mid-day sun, or use of a broad-brimmed hat, lip balm with anti UVA and UVB ingredients (e.g. para-aminobenzoic acid), or sun blocking agents (e.g. zinc oxide, titanium oxide) prior to sun exposure.

Schamberg's disease, (also known as "progressive pigmentary dermatosis of Schamberg", "purpura pigmentosa progressiva" (PPP), and "Schamberg's purpura") is a chronic discoloration of the skin found in people of all ages, usually affecting the legs. It slowly spreads throughout the body, and is most common in males. It is named after Jay Frank Schamberg, who described it in 1901. There is no known cure for this disease and it is not a life-threatening condition. The skin lesions may cause itching, which can be treated by applying cortisone cream. The cortisone cream will only help with the itching and the discoloration of the skin will remain, which may cause a cosmetic concern in the future. Schamberg's disease is usually asymptomatic meaning that it shows no signs of this condition, except for the discoloration of the skin. This condition is caused by leaky blood vessels, where red blood cells escape near the surface of skin and release its iron into the surrounding tissue. The cause of the leaky capillaries is unknown.

Pimple-popping, or Zit-popping, is the act of bursting or popping pimples with one's finger. Pimple-popping can lead to the introduction of bacteria into the pimple, infection, the creation of more pimples, and permanent scarring. Thus, popping is usually deprecated by dermatologists and estheticians and it is recommended to let the pimples run through their life span.

The most effective prevention is to grow a beard. For men who are required to; or simply prefer to shave, studies show the optimal length to be about 0.5 mm to 1 mm to prevent their hair growing back into the skin. Using a beard trimmer at the lowest setting (0.5mm or 1mm) instead of shaving is an effective alternative. The resulting faint stubble can be shaped using a standard electric razor on non-problematic areas (cheeks, lower neck).

For most cases, completely avoiding shaving for three to four weeks allows all lesions to subside, and most extrafollicular hairs will resolve themselves in about ten days.

Permanent removal of the hair follicle is the only definitive treatment for PFB. Electrolysis is effective but limited by its slow pace, pain and expense. Laser-assisted hair removal is effective. There is a risk of skin discoloration and a very small risk of scarring.

Exfoliation with various tools such as brushes and loofahs also helps prevent bumps.

Some men use electric razors to control PFB. Those who use a razor, should use a single blade or special wire-wrapped blade to avoid shaving too closely, with a new blade each shave. Shaving in the direction of hair growth every other day, rather than daily, may improve pseudofolliculitis barbae. If one must use a blade, softening the beard first with a hot, wet washcloth for five minutes or shave while showering in hot water can be helpful. Some use shaving powders (a kind of chemical depilatory) to avoid the irritation of using a blade. Barium sulfide-based depilatories are most effective, but produce an unpleasant smell.

Exogenous ochronosis can be caused from long-term usage of certain "skin lightening" products, even if the hydroquinone is in amounts as small as 2%.

Skin lightening products are still prevalent in many parts of the world. This may be due to aesthetic or social standing reasons, in areas where a lighter skin tone is considered to be a sign of wealth or beauty.

As well, skin-lightening creams containing compounds such as hydroquinone are commonly used to help with hyperpigmentation disorders such as melasma.

Hydroquinone is the compound most frequently used in skin whitening products. Due to concerns about its side effects, it was almost banned by the FDA in 2006, as there were medical issues of carcinogenicity and reports of disfiguring ochronosis. In the European Union hydroquinone has been banned in cosmetic creams since 2000.

Long-term use of creams containing this compound may lead to exogenous ochronotic lesions. The duration of the use is directly proportional to the risk of developing the condition with most cases being after years of use.

Around 10–15 million skin lightening products are sold annually, with Japan being the major buyer.

Practicing good hygiene, including regularly washing skin areas with neutral cleansers, can reduce the amount of dead skin cells and other external contaminants on the skin that can contribute to the development of pimples. However, it is not always possible to completely prevent pimples, even with good hygiene practices as a number of externalities such as hormones and genetics are at play.

Dermatosis neglecta is a skin condition in which accumulation of sebum, keratin, sweat, dirt and debris leads to a localized patch of skin discoloration or a wart-like plaque. It is caused by inadequate hygiene of a certain body part, usually due to some form of disability or a condition that is associated with pain or increased sensitivity to touch (hyperesthesia) or immobility.

Dermatosis neglecta typically develops several months after a disability or other affliction leads to improper cleaning. Patients may deny that negligence is the cause of the lesion, even though it completely resolves on vigorous rubbing with alcohol swabs or water and soap (which provides both diagnosis and treatment). Recognizing the diagnosis avoids unnecessary skin biopsies.

Examples of case reports from the literature include a man who avoided washing the skin area surrounding an artificial pacemaker out of fear it might be damaged; a woman who didn't clean the right side of her chest due to hyperesthesia following an amputation for breast cancer (mastectomy); a girl who was afraid to wash the area around an abdominal scar; and a man with multiple fractures, shoulder dislocation and radial nerve palsy which significantly reduced his mobility.

Poikiloderma of Civatte is a cutaneous condition and refers to reticulated red to red-brown patches with telangiectasias. It is identifiable as the reddish brown discoloration on sides of the neck, usually on both sides. It is more common with women than men and more commonly effects middle-aged to elderly women. "Poikiloderma" is basically a change of the skin due to dilation of the blood vessels in the neck. "Civatte" was the French dermatologist who first identified it in the 1920s.

DPN is not a premalignant condition nor is it associated with any underlying systemic disease. DPN lesions show no tendency to regress spontaneously, and often increase in size and number as an individual ages.

Treatment is predominantly preventive. Avoidance of topical phenols and diets low in tyrosine may help. Replacement and repair of damaged tissue is also possible.

DPN affects up to 35% of the African American population in the USA Insufficient data is available on the international frequency of DPN.

Lesions generally emerge during puberty, increasing steadily in number and size as an individual ages.

Black people with a fair complexion have the lowest frequency of involvement. DPN also occurs among Asians, although the exact incidence is unknown. Females are affected more frequently than males. Dermatosis papulosa nigra generally emerges in adolescence and is rarely in persons younger than 7 years The incidence, size and number of lesions of DPN increases with age.

Studies have recorded an incidence of about 3–5 cases per 1,000 newborn babies.

Disease states associated with carotenoderma include hypothyroidism, diabetes mellitus, anorexia nervosa, nephrotic syndrome, and liver disease. In hypothyroidism and diabetes mellitus, the underlying mechanism of hypercarotenemia is thought to be both impaired conversion of beta-carotene into retinol and the associated increased serum lipids. Diabetes mellitus has also been associated with carotenoderma through disease-specific diets that are rich in vegetables. In the nephrotic syndrome, the hypercarotenemia is related to the associated increased serum lipids, similar to the above entities.

It is of note that kidney dysfunction in general is associated with hypercarotenemia as a result of decreased excretion of carotenoids. Liver dysfunction, regardless of origin, causes hypercarotenemia as a result of the impaired conversion of carotenoids to retinol. This is of particular interest because jaundice and carotenoderma can coexist in the same patient. Anorexia nervosa causes carotenoderma mainly through diets that are rich in carotenoids and the associated hypothyroidism. It tends to be more common in the restricting subtype of this disease, and is associated with numerous other dermatologic manifestations, such as brittle hair and nails, lanugo-like body hair, and xerosis. Although Alzheimer's disease has been associated with carotenoderma in some reports, most studies on serum carotenoids in these patients show that their levels of carotenoids and retinol are depressed, and may be associated with the development of dementia. A true association between Alzheimer's disease and carotenoderma is unclear at this time. There have been case reports in the literature of increased serum carotenoids and carotenoderma that is unresponsive to dietary measures, with a genetic defect in carotenoid metabolic enzymes proposed. Canthaxanthin and astaxanthin are naturally occurring carotenoids that are used in the British and US food industry to add color to foods such as sausage and fish. Canthaxanthin has been used in over-the-counter “tanning pills” in the United States and Europe, but is not currently Food and Drug Administration (FDA)-approved for this purpose in the United States because of its adverse effects. These include hepatitis, urticaria, aplastic anemia, and a retinopathy characterized by yellow deposits and subsequent visual field defects.

Infants and small children are especially prone to carotenoderma because of the cooked, mashed, and pureed vegetables that they eat. Processing and homogenizing causes carotene to become more available for absorption. A small 2.5 ounce jar of baby food sweet potatoes or carrots contains about 400-500% of an infant's recommended daily value of carotene. In addition to that source of carotene, infants are usually prescribed a liquid vitamin supplement, such as Tri-Vi-Sol, which contains vitamin A.

Livedo racemosa is a cutaneous condition characterized by a skin discoloration appearing as irregular-broken circles.

Lycopenemia is a harmless skin condition caused by excessive ingestion of red foods, such as tomatoes, beets, chili beans, and various fruits and berries, which leads to a reddish discoloration of the skin.