Prurigo Simplex and Nodularis: Why the Itch Will Not Stop

Prurigo is a condition in which there are independent itchy papular/nodular eruptions induced by insect bite or allergy. These pruritic papules are thought to be an inflammatory response and are characterized by exudative inflammatory lesions that do not develop into the other types of eruptions e.g. psoriatic or eczematous lesions. Prurigo remains as chronic papules and nodules.

What makes prurigo so difficult to live with is not the bumps themselves but the itch. It is a deep, unreachable itch that does not settle with scratching — scratching only hardens the lesion and makes the next itch worse. That loop is the thing treatment has to break.

[1] Acute Prurigo (Strophulus Infantum) is when urticarial erythema or wheals appear and become exudative papules, usually in small children. Secondary infection may be caused by rubbing and scratching brought on by intense itching.

[2] Subacute Prurigo (Prurigo Simplex Subacute) is when an urticarial papule accompanied by intense itching occurs on the extensor surface of the extremities or the trunk. When it is rubbed and scratched, erosion or crust forms. A primary disease is often involved in Subacute Prurigo, for example, atopic dermatitis, diabetes, liver dysfunction, lymphoma, leukemia, Hodgkin’s disease, internal malignancy, polycythemia, gout, uremia or pregnancy. Sometimes, even mental stress can be associated with onset.

[3] Chronic Prurigo either presents as Prurigo Chronica Multiformis or Prurigo Nodularis. Prurigo chronica multiformis occurs most frequently in the trunk and legs of the elderly. Excoriation of these pruritic lesions create solid or exudative papules that aggregate to form plaques or lichenoid lesions.

Prurigo nodularis most commonly affects adolescents and older women. Papules and nodules occur in the extremities, accompanied by intense itching. When rubbed they develop erosion and bloody crusts, resulting in dark brown solid papules or nodules. These are different from Prurigo Chronica Multiformis in that they are isolated and do not aggregate to form plaques.

The nodules are typically firm, dome-shaped and a few millimetres to a couple of centimetres across. They cluster where the hand can easily reach — the outer arms, the shins, the upper back — and the middle of the back, where it cannot, is often conspicuously spared. That sparing is one of the clearest signs that scratching is driving the lesions rather than the other way round.

Prurigo looks different on brown and black skin, and that is a common reason it gets missed or mislabelled.

The redness that textbooks describe is hard to see through more pigmented skin. Instead the nodules tend to read as grey-brown, violet, or almost black. They often look firmer and more raised. The marks left behind — post-inflammatory hyperpigmentation — are darker, more obvious, and last considerably longer, frequently for months after the itch itself has settled.

Prurigo nodularis is also reported more frequently in people of African descent. If you have darker skin and have been told your nodules are ‘just scars’ or ‘just eczema’, it is worth having them looked at again.

In children, prurigo usually appears as papular urticaria, the form also called strophulus infantum. It typically follows insect bites — mosquitoes, fleas, mites — and comes up in crops on the exposed limbs, often with new lesions appearing as older ones fade.

It is usually self-limiting. The problem is the itch-scratch cycle: a child scratches through the papule, the skin breaks, and secondary bacterial infection follows. Keeping nails short and treating the itch early matters more than treating the bumps themselves.

Prurigo of pregnancy usually appears in the second or third trimester as itchy papules on the limbs. It is uncomfortable but it is not dangerous to the baby, and it generally settles after delivery.

One thing to be careful about. Intense itching in pregnancy without a rash — particularly on the palms and soles, and often worse at night — can be intrahepatic cholestasis of pregnancy, which is a different condition and does carry risk to the baby. That needs a doctor and a blood test, not a herbalist. If you are pregnant and itching without a visible rash, get it checked.

In modern Chinese medical use, prurigo is 痒疹 (yǎng zhěn) — literally an itch rash.

• 结节性痒疹 (jié jié xìng yǎng zhěn) — prurigo nodularis, ‘nodular itch rash’
• 丘疹性荨麻疹 (qiū zhěn xìng xún má zhěn) — papular urticaria, the childhood form after insect bites

The classical dermatology texts are more descriptive. Prurigo nodularis is 顽湿聚结 (wán shī jù jié) — stubborn damp gathering and knotting together, which is a fair description of what a nodule actually is. The older term 粟疮 (sù chuāng), ‘millet sore’, describes the smaller seed-like papules.

Prurigo is not cancer, and it does not turn into cancer. The nodules are the skin’s response to being scratched over and over, not a tumour.

It is also not classified as an autoimmune disease, though it is immune-mediated — the itch pathway and the nerve endings in the skin are both involved.

What is worth taking seriously is the company prurigo sometimes keeps. As above, subacute prurigo can sit alongside a primary disease — liver dysfunction, kidney disease, diabetes, thyroid disease, iron deficiency, and occasionally lymphoma or another internal malignancy. If persistent prurigo appears in an adult with no obvious trigger, that deserves a proper workup rather than another tube of cream.

Prurigo nodules commonly leave dark marks once they flatten. These are post-inflammatory hyperpigmentation rather than true scars, and on most skin they fade over months. On darker skin they take longer.

True scarring happens where the nodule has been picked or excoriated repeatedly and the skin has been broken to depth. That is another reason to treat the itch aggressively and early — the sooner the scratching stops, the less there is to fade.

Apart from sub acute prurigo, where treatment of the primary disease is crucial, this disease is usually managed with steroid and antihistamines, and sometimes even with immune-suppressants. The mainstay of treatment at our clinic is the management of inflammation with acupuncture treatment and herbal therapy.

In Chinese medicine terms the presentation is usually read as damp and heat lodged in the skin, with wind driving the itch, and — in longstanding nodules — blood stasis holding the lesion in place. The herbs are chosen against that pattern rather than against the label, which is why two people with the same diagnosis do not necessarily leave with the same prescription.

What we are aiming at first is the itch. Once the itch drops far enough that the hand stops going to the skin, the nodules have a chance to flatten on their own.