What is the difference between psoriasis and ringworm?

Psoriasis is characterised by the presence of red, scaly patches that form on specific areas of the body. These patches can cause itching and irritation, with the intensity varying between individuals. They emerge in response to a skin inflammation caused by a malfunction of the immune system. T lymphocytes are responsible for the production of inflammatory molecules such as cytokines Il-17, Il-22, TNF-alpha and others. These substances stimulate the multiplication of keratinocytes, cells found in the skin. As a result, the normal rhythm of cell renewal, which would typically take three weeks, is accelerated to just three days. This process leads to an accumulation of immature keratinocytes on the skin's surface, which increases the thickness of the superficial layer, thus forming a hyperkeratosis.

The skin symptoms of psoriasis can affect any area of the body, from the ears to the tongue, including the genital areas, leading to various clinical forms. However, the scaly plaques are generally located on the scalp, elbows and knees. They are sometimes accompanied by a rheumatism.

Also known as tinea, dermatophyte infection or dermatophytosis, ringworm is a common and contagious fungal disease that affects the skin. It is caused by fungi known as dermatophytes, which feed on keratin, a protein found in skin tissues, hair and nails. The fungi are classified into three groups depending on where they are normally found. Geophilic organisms live in the soil, zoophilic organisms on animals, and anthropophilic organisms on humans. It manifests itself through a scaly circular rash in the shape of a ring, from which the disease gets its name.

Tinea corporis is a superficial dermatophyte infection that can affect the entire body, with the exception of certain areas. For these areas, the disease takes on other names:

• Tinea manuum for the hands;

• Athlete's foot for the feet;

• Tinea capitis in the scalp;

• Tina barbae in the bearded areas;

• Tinea faciei on the face.

Ringworm or psoriasis, here are the key elements that distinguish them:

• The primary cause.

  For psoriasis, it is a failure of the immune system and a genetic predisposition, whereas ringworm is of fungal origin.

• Infection.

  Ringworm is a contagious condition, spreading through physical contact, whether it be direct skin-to-skin contact, through an animal, or contaminated objects. On the other hand, psoriasis is not contagious.

• The symptoms.

  Ringworm and psoriasis can cause itching, patches, and flaking. However, psoriasis patches tend to thicken over a specific area. Those of ringworm typically present in a ring-like form and move from one region to another. Psoriatic patches may not cause itching. However, the blisters caused by ringworm are particularly irritating, compared to psoriasis.

• Location.

  Psoriasis can develop on various parts of the body such as the face, nails, scalp, elbows, etc. Ringworm primarily locates in areas where hair is present, for instance, the scalp or the beard.

• The diagnosis.

  The diagnosis of psoriasis is primarily based on the visual examination of skin plaques conducted by a dermatologist. The diagnosis of ringworm may require tests such as skin scrapings to search for the presence of fungi under a microscope.

• The treatments.

  These two dermatological conditions have different origins, which results in differences in their treatments. To treat psoriasis, it is possible to turn to treatments that are topical and contain anti-inflammatory and keratolytic active ingredients. Moreover, phototherapy can be beneficial for psoriasis. However, this is not the case for ringworm. As this condition is fungal in origin, the treatments used are therefore topical care or oral medications based on antifungal agents.

FULLER L. C. & al. Diagnosis and management of scalp ringworm. Clinical review (2003).

MSEDDI M. & al. Les teignes de l’adulte : étude rétrospective dans le sud Tunisien. Journal de Mycologie Médicale (2005).

OHTSUKI M. & al. Risk Factors for the Development of Psoriasis International Journal of Molecular Sciences (2019).