Prurigo nodularis (PN) is extremely itchy skin that leads to a bumpy rash. The rash appears as the result of repeated scratching, picking, or rubbing of the itchy areas of the skin.

There isn’t one single cause of PN. Sometimes, the itching that leads to a rash is a symptom of an underlying condition, such as hepatitis C or lymphoma. PN can also occur on its own.

The itch-scratch cycle is a key aspect of PN. Itchiness prompts a scratch response, and scratching causes future itchiness. Reducing this cycle is a goal of PN treatment.

Read on to learn answers to frequently asked questions about prurigo nodularis.

Prurigo nodularis is itchy, bumpy skin that differs from unaffected skin in several ways:

  • increased nerve sensitivity
  • the presence of inflammation
  • hypervascularization (increased number of blood vessels)
  • dermal fibrosis (increased fibrous connective tissue in the skin)
  • epidermal hyperkeratosis (skin thickening)

PN skin causes both nerve and immune system changes. There are a higher level of cytokines and their receptors active at the rash site, as well as in the central nervous system, for the transmission of itch signals. Cytokines are small signaling proteins produced by immune system cells.

There are several categories of itch that can trigger PN:

  • Dermatological: This is itching originating in the skin and is considered to be the most common trigger in PN, occurring in up to 82% of instances.
  • Systemic: This type of itch has its origin in non-skin areas of the body, like organs and blood.
  • Infectious: PN itch can have an infectious cause, like tuberculosis or H. pylori.
  • Medication-related: Some medications, like cancer therapy agents, can cause PN.
  • Psychiatric: PN can have mental health causes like anxiety, depression, or dissociative experiences. This is different from dermatillomania, which is a skin-picking impulse disorder.
  • Neurologic: Nerve damage like compression or degeneration can sometimes cause PN.

When a PN rash appears, it’s usually in areas that are easy to scratch, such as:

  • abdomen
  • arms and legs
  • buttocks
  • lower and upper back

It’s common for the bumps to appear equally on both sides of the body.

The size and color of the rash nodules can vary. They can range in size from as small as a pinhead to larger than a quarter.

PN bumps can be brownish-black, red, or pink. Your skin color may affect the appearance of the rash. For example, Black people may have nodules that are firmer, darker, and larger.

Some people have a small number of bumps, while others have hundreds. You may also develop raised patches of skin or notice that your skin has hardened and thickened.

An untreated PN rash is itchy enough that people often scratch until they draw blood. The scratching causes more itching and more bumps, which can last for years and leave scars.

PN is not a virus.

However, sometimes a virus can be the cause of an underlying condition that leads to PN. Examples include HIV and viral hepatitis.

PN may also be associated with metabolic dysfunction, such as type 2 diabetes. It can also occur with organ, skin, and hematopoietic (blood) cancers.

PN isn’t a virus, metabolic disorder, or cancer. Instead, researchers believe it’s a result of immunological and neuronal changes in the body.

PN isn’t contagious, although an associated underlying condition may be transmissible.

HIV is one such example. It’s transmissible via bodily fluids, and a person who contracts HIV may or may not develop PN.

Viral hepatitis is another example. PN can develop in a person who has contracted the hepatitis virus.

Bacterial infections associated with PN include tuberculosis and H. pylori.

Parasitic infections, such as strongyloidiasis, are also associated with PN.

It’s not clear whether PN can become cancer, although it can be an indicator that cancer is present somewhere in the body.

A 2019 study found that certain types of cancer occurred more often in people with PN than in PN-free controls. It also found that improvements in PN symptoms occurred with cancer treatment.

The study indicated that the most common cancers connected to PN are skin cancers:

  • squamous cell carcinoma
  • basal cell carcinoma
  • malignant melanoma

The study found that the second most common category of cancer connected to PN is hematopoietic, or blood cancers:

  • non-Hodgkin’s lymphoma
  • multiple myeloma
  • primary cutaneous lymphoma
  • myeloid leukemia
  • lymphocytic leukemia
  • Hodgkin’s lymphoma

Solid organ cancers can also occur with PN, some of which include:

  • female genital organs
  • lung
  • gastrointestinal tract
  • breast
  • head and neck
  • urinary tract
  • endocrine glands

These cancers don’t always trigger PN.

Also, if you have PN, it doesn’t mean you have cancer. However, your dermatologist may order tests to make sure.

PN can be the first sign of an underlying condition, like HIV or lymphoma. Finding the correct diagnosis is an important step in treating PN, so your dermatologist may conduct tests or bloodwork.

The itch-scratch cycle is an important component of understanding PN. This refers to the way that itching prompts scratching, which in turn causes more itch. Calming the itch-scratch cycle is an important part of PN treatment.

There are a variety of treatment options for prurigo nodularis.

  • topical itch relief, like anti-itch emollients, phenol, menthol, pramoxine, or capsaicin
  • calcipotriol, a vitamin D derivative that slows skin cell production
  • topical anti-inflammatory medication, like corticosteroids, tacrolimus, pimecrolimus, or calcipotriol
  • cryosurgery
  • corticosteroid injections
  • phototherapy
  • systemic medication, like antihistamines, monoclonal antibodies, or medications for nerve pain
  • mental health support

There’s one Food and Drug Administration (FDA)-approved medication for PN: the monoclonal antibody dupilumab (Dupixent). It’s an injectable treatment that reduces inflammation by controlling cytokine signaling.

PN is a condition involving intense itching or skin discomfort that leads to symmetrically distributed bumps in varying sizes and numbers. It can occur on its own or in the presence of an associated underlying condition.

Although it’s not a virus and not contagious, PN can be triggered by conditions that are, such as HIV and viral hepatitis. It’s also associated with several types of cancer.

PN can sometimes be the first sign of an underlying condition, so a thorough assessment is important for a proper diagnosis. An important goal of treatment is to reduce the number and size of skin nodules by calming the itch-scratch cycle.