Sometimes irregular tan lines or unexpected allergic reactions leave a person's skin looking out of the ordinary. Other times, a common skin condition such as psoriasis (pictured) or eczema might affect a person's appearance. But some folks have health conditions that result in permanently atypical skin. From discolorations to mystery sensations, keep clicking for a look at 9 uncommon skin conditions, with help from the National Institutes of Health and First Skin Foundation...

What is Morgellons disease? It's still a mystery. The condition was established after dozens of anecdotal reports of people experiencing symptoms that include crawling, biting and stinging sensations on the skin; skin lesions, rashes or sores; and some mental confusion. A 2012 study yielded no answers explaining the disease, which many doctors believe exists only in patients' minds.

The CDC recommends seeing a doctor who can treat co-existing medical, including psychiatric conditions, that might be contributing to their symptoms.

Vitiligo is a skin condition in which there is a loss of brown pigment from certain areas of skin, leading to irregular white patches. It affects about one per 100 people in the U.S. Vitiligo occurs when immune cells destroy the cells that produce brown pigment, and is thought to be an autoimmune problem.

Vitiligo is tough to treat. But cosmetics can help, and there are a number of treatments that can minimize, camouflage, or even eliminate the white patches. These include steroid creams and a treatment known as photochemotherapy, in which drugs and ultraviolet light are used in combination. For people with vitiligo on more than 50 percent of their bodies, there's depigmentation, in which patients apply a drug that fades the skin to match the depigmented areas.

Erythropoietic protoporphyria, known as EPP, is a disease characterized by extreme sensitivity to light. Patients with EPP feel a burning sensation in their skin, and experience redness and swelling. As a result, they typically have to avoid exposure to strong light and must wear appropriate protection when they're in the sun.

Besides avoiding the sun, treatments for symptoms include pain medication, sedatives, beta-carotene supplements, fluids and glucose to boost carbohydrate levels.

Harlequin ichthyosis is a severe genetic disorder that results in thick skin spotted with deep cracks. These skin abnormalities affect the shape of facial features and limit arm and leg movement. Harlequin ichthyosis also makes it difficult for patients - particularly infants - to control their body temperature and fight infection. Infants with the disorder often develop life-threatening infections in the first few weeks of life.

It used to be very rare for affected infants to survive the newborn period, but improved treatment has increased patients' chances of into adolescence. It can be treated with drugs called retinoids, which are synethic forms of Vitamin A, under a dermatologist's supervision.

Blau syndrome is a rare condition characterized by skin rash, arthritis and swelling in the eye. People with Blau syndrome tend to have fluid in their joints, and sometimes have permanent bending of the fingers and toes. It is an autosomal disease caused by genetic mutations.

Blau syndrome can't be cured, but doctors will sometimes treat patients with immunosuppressant medications to reduce symptoms.

Epidermolytic ichthyosis is another type of icthyosis - a family of genetic skin disorders - characterized by redness and scales on the skin, especially around large joints. Blistering caused by infection is common, though it tends to get better with age - although scaling is lifelong.

Ichthyosis en confetti, or with confetti, is a skin condition resulting in red skin speckled with spots of pale, normal skin cells ("confetti"). The genetic disorder is extremely rare.

According to Nature News, the disease manages to "cure itself" in some patients by what researcher theorize to be "natural selection under the skin," in which cells spontaneously mutate to grow new healthy patches of skin.

Lamellar icthyosis is a type of icthyosis in which a baby is born with a tight, clear sheath covering their skin (called a collodion membrane). It is usually shed within the first few weeks of life, leaving scaly skin - the scales are usually large, dark and plate-like. Lamellar ichthyosis affects an estimated 1 in 200,000 to 300,000 people in the U.S.

Moisturizers containing urea, ammonium lactate, or other alpha-hydroxy acids may help, as well as retinoids which are often used to treat ichthyosis.