Symptoms include:

1. yellow-brown, banana-shaped fibers

2. caviar-like papules

3. brown-grey or blue-black hyper-pigmentation

The majority of the lesions will be seen on areas of the body that get the most sun.

There are two types of ochronosis: endogenous and exogenous. The endogenous variety is an autosomal recessive disease, that is caused by a lack of homogentisate oxidase enzyme.

Exogenous ochronosis is an avoidable dermatitis, that can be caused by the topical application of compounds such as hydroquinone or phenols.

It was first seen in 1912, when a patient who used phenol on a leg ulcer was found by Beddard and Plumtre to have this condition.

Hydroquinone-induced exogenous ochronosis was found in 1975 by Findlay, who observed the condition in patients who used skin lightening creams containing the compound.

There are three clinical stages of exogenous ochronosis:

1. erythema and mild hyperpigmentation

2. hypergimentation and "caviar-like" lesions

3. papulo-nodular lesions

Patients with black bone disease are asymptomatic as children or young adults, but their urine may turn brown or even inky black if collected and left exposed to open air. Pigmentation may be noted in the cartilage of the ear as well as other cartilage, and the sclera and corneal limbus of the eye.

After the age of thirty people begin to develop pain in the weight-bearing joints of the spine, hips and knees. The pain can be severe to the point that interferes with activities of daily living and may affect ability to work. Joint replacement surgery (hip and shoulder) is often necessary at a relatively young age. In the longer term, the involvement of the spinal joints leads to reduced movement of the rib cage and can affect breathing. Bone mineral density may be affected, increasing the risk of bone fractures, and rupture of tendons and muscles may occur.

Valvular heart disease, mainly calcification and regurgitation of the aortic and mitral valves, may occur, and in severe and progressive cases valve replacement may be necessary. Irregularities in the heart rhythm and heart failure affect a significant proportion of people with alkaptonuria (40% and 10% respectively). Hearing loss affects 40% of people. There is also a propensity to developing kidney stones, and eventually also gallstones and stones in the prostate and salivary glands (sialolithiasis).

Alkaptonuria is a rare inherited genetic disorder in which the body cannot process the amino acids phenylalanine and tyrosine, which occur in protein. It is caused by a mutation in the "HGD" gene for the enzyme homogentisate 1,2-dioxygenase (); if a person inherits abnormal copies from each parent (it is a recessive condition) the body accumulates an intermediate substance called homogentisic acid in the blood and tissues. Homogentisic acid and its oxidized form "alkapton" are excreted in the urine, giving it an unusually dark color. The accumulating homogentisic acid causes damage to cartilage (ochronosis, leading to osteoarthritis) and heart valves as well as precipitating as kidney stones and stones in other organs. Symptoms usually develop in people over thirty years old, although the dark discoloration of the urine is present from birth.

Apart from treatment of the complications (such as pain relief and joint replacement for the cartilage damage), the drug nitisinone has been found to suppress homogentisic acid production, and research is ongoing as to whether it can improve symptoms. Alkaptonuria is a rare disease; it occurs in one in 250,000 people, but is more common in Slovakia and the Dominican Republic.

Generally, the areas affected are exposed skin not usually protected by clothing; however it can also occur in areas covered by clothing. Areas constantly subjected to the sun's rays may only be slightly affected if at all. People with extreme cases will also have reactions to light bulbs that emit a UV wavelength (any bulb that is not an LED). Parts of the body only thinly covered can also potentially be subjected to an outbreak.

Life with SU can be difficult. Patients are subject to constant itching and pain, as within minutes of the initial exposure to UV radiation a rash will appear. The urticarial reaction begins in the form of pruritus, later progressing to erythema and edema in the exposed areas of the skin. If vast areas of the body are affected, the loss of fluid into the skin could lead to light-headedness, headache, nausea, and vomiting. Extremely rarely, patients have been reported to experience an increase in heart rate that can cause a stroke or heart attack due to the body cavity swelling. Other rare side effects can be bronchospasm and glucose instability issues. Also, if a large area of the body is suddenly exposed the person may be subject to an anaphylactic reaction. Once free of exposure, the rash will usually fade away within several hours; rare and extreme cases can take a day or two to normalize depending on severity of the reaction.

Steroid acne is an adverse reaction to corticosteroids, and presents as small, firm follicular papules on the forehead, cheeks, and chest. Steroid acne presents with monomorphous pink paupules, as well as comedones, which may be indistinguishable from those of acne vulgaris. Steroid acne is commonly associated with endogenous or exogenous sources of androgen, drug therapy, or diabetes and is less commonly associated with HIV infection or Hodgkin's disease.

Signs and symptoms of AIP can be variable. Severe and poorly localized abdominal pain is a very common symptom (found in 95% of those affected by AIP). Urinary signs and symptoms such as painful urination, urinary retention, urinary incontinence, or dark urine have also been known to occur. Psychiatric signs and symptoms of AIP may manifest as anxiety, paranoia, irritability, delusions, hallucinations, confusion, and depression. Signs that suggest increased activity of the sympathetic nervous system may be evident including tachycardia, hypertension, palpitations, orthostatic hypotension, sweating, restlessness, and tremor. Other neurologic signs and symptoms of AIP include seizures, peripheral neuropathy, abnormal sensations, chest pain, leg pain, back pain or headache, and coma. Nausea, vomiting, constipation, and diarrhea can also occur. Proximal muscle weakness typically beginning in the arms is characteristic; there can be muscle pain, tingling, numbness, weakness or paralysis; muscle weakness seen in AIP can progress to include the muscles of breathing causing respiratory failure and can be fatal.

AIP patients have an increased risk of developing hepatocellular carcinoma, melanoma, lymphoma, chronic hypertension, chronic kidney disease, and chronic pain.

Polymorphous light eruption (PMLE) is the easiest disease to mistake for solar urticaria because the locations of the lesions are similar (the V of the neck and the arms). However, patients with SU are more likely to develop lesions on the face. Also, a reaction with PMLE will take a greater amount of time to appear than with solar urticaria. Lupus erythematosus has been mistaken for SU; however, lesions from lupus erythematosus will take a longer amount of time to go away. Furthermore, when being tested for the two diseases, patients with SU have a reaction immediately while patients with lupus erythematosus will have a delayed reaction. Patients who have experienced solar urticarial symptoms from a young age could mistakenly be thought to have erythropoietic protoporphyria. However, the main symptom for this disease is pain and patients with have been found to have abnormal levels of protoporphyrin in their blood while these levels are normal in SU patients. Finally, cholinergic urticaria, or urticaria induced by heat, can occasionally appear to be solar urticaria because the heat from the sun will cause a person with the disease to have a reaction.

Signs and symptoms of methemoglobinemia (methemoglobin level above 10%) include shortness of breath, cyanosis, mental status changes (~50%), headache, fatigue, exercise intolerance, dizziness and loss of hairlines.

Patients with severe methemoglobinemia (methemoglobin level above 50%) may exhibit seizures, coma and death (>70%). Healthy people may not have many symptoms with methemoglobin levels below 15%. However, patients with co-morbidities such as anemia, cardiovascular disease, lung disease, sepsis, or presence of other abnormal hemoglobin species (e.g. carboxyhemoglobin, sulfhemoglobin or sickle hemoglobin) may experience moderate to severe symptoms at much lower levels (as low as 5–8%).

Amalgam tattoo (also termed localized argyrosis, or focal argyrosis) is a grey, blue or black area of discoloration on the mucous membranes of the mouth, typically on the gums of the lower jaw. It is an iatrogenic lesion, caused by entry of dental amalgam into the soft tissues. It is common, painless, and benign, but it can be mistaken for melanoma.

Amalgam tattoo usually occurs on the mandibular gingiva, often in an area in which a apicoectomy ("root-end filling") with amalgam was carried out. After the gingiva, the alveolar mucosa and the buccal mucosa are the next most common sites, although any mucosal site in the mouth is possible. It is painless, and appears as a blue-black or grey discolored macule on the surface of the mucosa. The borders of the tattoo are variable, and may be well defined, irregular or diffuse.

Methemoglobinemia is a condition caused by elevated levels of methemoglobin in the blood. Methemoglobin is a form of hemoglobin that contains the ferric [Fe] form of iron. The affinity for oxygen of ferric iron is impaired. The binding of oxygen to methemoglobin results in an "increased" affinity for oxygen in the remaining heme sites that are in ferrous state within the same tetrameric hemoglobin unit. This leads to an overall reduced ability of the red blood cell to release oxygen to tissues, with the associated oxygen–hemoglobin dissociation curve therefore shifted to the left. When methemoglobin concentration is elevated in red blood cells, tissue hypoxia may occur.

Pain and itch have very different behavioral response patterns. Pain evokes a withdrawal reflex, which leads to retraction and therefore a reaction trying to protect an endangered part of the body. Itch in contrast creates a scratch reflex, which draws one to the affected skin site. Itch generates stimulus of a foreign object underneath or upon the skin and also the urge to remove it. For example, responding to a local itch sensation is an effective way to remove insects from one's skin.

Scratching has traditionally been regarded as a way to relieve oneself by reducing the annoying itch sensation. However, there are hedonic aspects of scratching, as one would find noxious scratching highly pleasurable. This can be problematic with chronic itch patients, such as ones with atopic dermatitis, who may scratch affected spots until they no longer produce a pleasant or painful sensation, instead of when the itch sensation disappears. It has been hypothesized that motivational aspects of scratching include the frontal brain areas of reward and decision making. These aspects might therefore contribute to the compulsive nature of itch and scratching.

Acute intermittent porphyria (AIP) is a genetic metabolic disorder affecting the production of heme, the oxygen-binding prosthetic group of hemoglobin. It is characterized by a deficiency of the enzyme porphobilinogen deaminase. Its inheritance is more commonly autosomal dominant; however, autosomal recessive forms of this disorder have occurred. Its incidence is estimated to be between 5 and 10 in 100,000.

Patients may present with features of hypocalcaemia including carpo-pedal muscular spasms, cramping, tetany, and if the calcium deficit is severe, generalized seizures. IQ is typically mildly depressed or unaffected. Additional characteristics include short stature, obesity, developmental delay, and calcification of the basal ganglia in the deep white matter of the brain.

Type 1a Pseudohypoparathyroidism is clinically manifest by bone resorption with blunting of the fourth and fifth knuckles of the hand, most notable when the dorsum of the hand is viewed in closed fist position. This presentation is known as 'knuckle knuckle dimple dimple' sign (Archibald's Sign). This is as opposed to Turner syndrome which is characterized by blunting of only the fourth knuckle, and Down's syndrome, which is associated with a hypoplastic middle phalanx.

The term pseudopseudohypoparathyroidism is used to describe a condition where the individual has the phenotypic appearance of pseudohypoparathyroidism type 1a, but is biochemically normal.

Events of "contagious itch" are very common occurrences. Even a discussion on the topic of itch can give one the desire to scratch. Itch is likely to be more than a localized phenomenon in the place we scratch. Results from a study showed that itching and scratching were induced purely by visual stimuli in a public lecture on itching. The sensation of pain can also be induced in a similar fashion, often by listening to a description of an injury, or viewing an injury itself.

There is little detailed data on central activation for contagious itching, but it is hypothesized that a human mirror neuron system exists in which we imitate certain motor actions when we view others performing the same action. A similar phenomenon in which mirror neurons are used to explain the cause is contagious yawning.

Plasma cell cheilitis is a very rare presentation of a condition which more usually occurs on the gingiva (termed "plasma cell gingivitis") or sometimes the tongue. Plasma cell cheilitis appears as well defined, infiltrated, dark red plaque with a superficial lacquer-like glazing. Plasma cell cheilitis usually involves the lower lip. The lips appear dry, atrophic and fissured. Angular cheilitis is sometimes also present.

Bacterial skin infections include:

- Folliculitis is an infection of the hair follicle that can resemble pimples.

- Impetigo is a highly contagious bacterial skin infection most common among pre-school children. It is primarily caused by "Staphylococcus aureus", and sometimes by "Streptococcus pyogenes".

- Erysipelas is an acute streptococcus bacterial infection of the deep epidermis with lymphatic spread.

- Cellulitis is a diffuse inflammation of connective tissue with severe inflammation of dermal and subcutaneous layers of the skin. Cellulitis can be caused by normal skin flora or by exogenous bacteria, and often occurs where the skin has previously been broken: cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, intravenous drug injection or sites of intravenous catheter insertion. Skin on the face or lower legs is most commonly affected by this infection, though cellulitis can occur on any part of the body.

Common causes of drug-related cheilitis include Etretinate, Indinavir, Protease inhibitors, Vitamin A and Isotretinoin (a retinoid drug). Uncommon causes include Atorvastatin, Busulphan, Clofazimine, Clomipramine, Cyancobalamin, Gold, Methyldopa, Psoralens, Streptomycin, Sulfasalazine and Tetracycline. A condition called "drug-induced ulcer of the lip" is described as being characterized by painful or tender, well-defined ulcerations of the lip without induration. It is the result of oral administration of drugs, and the condition resolves when the drugs are stopped.

A common cause of chondrocalcinosis is calcium pyrophosphate dihydrate crystal deposition disease (CPPD).

Excessive calcium (due to hypomagnesemia) has a potential relationship with chondrocalcinosis, and magnesium supplementation may reduce or alleviate symptoms. In some cases, arthritis from injury can cause chondrocalcinosis.

Other causes of chondrocalcinosis include:

- Hypercalcaemia, especially when caused by hyperparathyroidism

- Arthritis

- Gout

- Wilson disease

- Hemochromatosis

- Ochronosis

- Hypothyroidism

- Hyperoxalemia

- Acromegaly

- osteoarthritis

Infection of the skin is distinguished from dermatitis, which is inflammation of the skin, but a skin infection can result in skin inflammation. Skin inflammation due to skin infection is called "infective dermatitis."

Bacterial skin infections affected about 155 million people and cellulitis occurred in about 600 million people in 2013.

Characterized by dermal edema (wheal) and erthema (flare) also known as hives. Hive lesions typically last less than 24 and are usually pruritic. Hives can appear on anywhere on the body and they may change shape, move around, disappear and reappear over short periods of time.

Acute urticaria (short-term): can develop suddenly and will last "less" than 6 weeks. About 1 in 6 people will have acute hives at one point in their life.

Chronic urticaria (long-term): can develop suddenly and will persist "more" than 6 weeks. This type of urticaria is uncommon and occurs in only 0.1% of the population. 20% of people with chronic urticaria report still having problems 10 years after its onset.

Chondrocalcinosis can be visualized on projectional radiography, CT scan, MRI, US, and nuclear medicine. CT scans and MRIs show calcific masses (usually within the ligamentum flavum or joint capsule), however radiography is more successful. At ultrasound, chondrocalcinosis may be depicted as echogenic foci with no acoustic shadow within the hyaline cartilage. As with most conditions, chondrocalcinosis can present with similarity to other diseases such as ankylosing spondylitis and gout.