Millions of Americans live with at least one skin condition. You’re probably familiar with the more common ones like acne, eczema, and rosacea. In fact, there’s a good chance you may have one of them yourself.

There is also a wide range of rarer skin conditions that you may not know about. They can range from mild to life-threatening. In some cases, they can affect the quality of life of those who develop them.

Read on for a brief overview of some of these lesser-known conditions.

Hidradenitis suppurativa (HS) is a chronic inflammatory condition that causes lesions to form on parts of the body where skin touches skin. The most common areas for breakouts to occur are the underarms, groin, buttocks, upper thighs, and breasts.

Although the cause of HS is unknown, it’s likely that hormones play a role in its development since it typically begins around puberty. It’s most common in people who are overweight or smoke, and women are three times more likely to have HS than men. The immune system is also believed to be a factor.

The initial symptoms of HS are breakouts that look like pimples or boils. These breakouts either stay on the skin or clear and then reappear. If left untreated, more severe symptoms can occur, such as scarring, infection, and breakouts that rupture and emit a foul-smelling fluid.

There is currently no cure for HS, but a number of treatment options are available to help manage symptoms. These include topical ointments, anti-inflammatory drugs (including biologics), hormone therapy, and in more severe cases, surgery.

Similar to HS, inverse psoriasis (also sometimes called intertriginous psoriasis) creates red lesions on parts of the body where skin touches skin. These lesions are not boil-like, but appear to be smooth and shiny. Many people with inverse psoriasis also have at least one other type of psoriasis somewhere else on their body as well.

Since the skin in these high-friction areas of the body tends to be sensitive, treating the condition can be difficult. Steroid creams and topical ointments may be effective but often cause painful irritation if overused.

People living with more severe cases of inverse psoriasis may also need ultraviolet B (UVB) light therapy or injectable biologic medications to manage their condition.

Harlequin ichthyosis is a rare genetic disorder that causes children to be born with hard, thick skin that forms diamond-shaped scales across their bodies. These plates, separated by deep cracks, can affect the shape of their eyelids, mouth, nose, and ears. They can also restrict movement of the limbs and chest.

The condition is caused by a mutation in the ABCA12 gene, which allows the body to make a protein essential for the normal development of skin cells. The mutation prevents the transportation of lipids to the epidermis and results in the scale-like plates, which make it more difficult to control water loss, regulate body temperature, and fight infection.

The most common treatment for harlequin ichthyosis is a strict regimen of skin-softening emollients and skin-repairing moisturizers. In severe cases, oral retinoid may also be used.

Morgellons disease is a rare condition in which small fibers and particles emerge from skin sores, creating the sensation that something is crawling on the skin. Little is known about the condition. Some doctors believe it’s a psychological issue since its symptoms are similar to a mental illness called delusional infestation.

Morgellons is most prevalent in middle-aged white women. Its most common symptoms are itchy skin rashes or sores, black fibrous material in and on the skin, anxiety, fatigue, and depression.

Since Morgellons disease is still not fully understood, there’s no standard treatment option. People with Morgellons are typically advised to keep in close contact with their healthcare team and seek treatment for side effects like anxiety and depression.

Elastoderma is a rare condition marked by increased laxity of the skin on specific areas of the body, causing the skin to sag or hang down in loose folds. It can occur on any part of the body, but the neck and the extremities, especially around the elbows and knees, are the most commonly affected areas.

The exact cause of elastoderma is unknown. It is thought to be the result of the overproduction of a protein called elastin that gives structural support to organs and tissues.

Due to the rarity of the condition, there’s currently no standard treatment for elastoderma. Some people will undergo surgery to remove the affected area, but the loose skin often returns following the operation.