Itchy rash

Itchy rash

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Rash: dermatitis and eczema

Itchy rash is a common symptom that can be caused by a variety of diseases, allergic reactions, or psychological problems. The rash appears as an acute and chronic symptom, in which those affected sometimes suffer significant impairments in everyday life depending on the cause, duration and location of the complaints. In addition, patients often have a reduced self-esteem, especially if it is a rash on the face. The skin irritation should best be examined by a specialist (dermatologist or dermatologist) in order to determine the causes and to rule out more serious diseases.


The itchy rash denotes a superficial irritation of the skin, which is described in the medical community under the terms dermatitis and eczema. Depending on the duration of the symptoms, a distinction must be made between acute and chronic skin rash, whereby the term exanthem is also used for the acute case.

A subdivision can also be made based on the visible skin changes, the so-called efflorescence. A distinction is made between primary fluorescence and secondary fluorescence. The primary efflorescences such as vesicles, blisters, wheals, pustules, nodules or so-called macula and plaque are caused directly by the pathological skin changes.

The secondary florescences such as skin flakes, incrustations, abrasions, ulcers and scars, on the other hand, only appear as a result of the primary florescences or human reactions to them. For example, injuries to the skin surface from the fingernails when scratching come into consideration.

Symptoms of an itchy rash

The rash described is usually characterized by severe itching and changes in the color and texture of the skin. The rash is often limited to certain areas of the body such as the face, armpits, elbows, back of the knees or the back, but can also occur across the entire body or in spots. Depending on the causes of the skin change, it takes different forms, with an expansion of the affected skin surface being not uncommon.

Typical signs of eczema

With eczema, the itchy rash, despite different causes, usually shows a typical sequence of symptoms that begins in the acute stage with a slight reddening of the skin (erythema), caused by increased blood circulation. With more severe reactions, it leads to the formation of bubbles with contained clear liquid. These burst easily and then release the liquid. When the burst bubbles dry, a crust forms, which then peels off the skin in a scaled manner.

The stage of vesicle formation is referred to as vesicolosum stage in the professional world. If the vesicles burst and begin to wet, the madidans stage has been reached. The subsequent crust formation marks the crustosum stage, followed by the squamosum stage, in which the scales detach. In the case of chronic eczema, the individual stages can repeat or occur at the same time. The skin also tends to swell and often shows a coarser skin structure.

As a result of the injuries, the skin surface is more susceptible to bacterial infections in eczema. These in turn can cause a further deterioration in the skin condition, which threatens a mutually reinforcing development of the disease processes.

Furthermore, fungal infections are promoted by the eczema, whereby even the yeast fungi that occur naturally on the skin can cause a corresponding infection. In rather rare cases, the skin disease in conjunction with herpes simplex viruses develops a so-called eczema herpeticatum. This can lead to life-threatening blood poisoning and must often be treated with hospital infusions.

Symptoms of an acute rash

An acute, itchy rash (rash) can be caused by various infectious diseases such as measles, rubella, scarlet fever or chickenpox. The rash usually takes a disease-specific form and is accompanied by various accompanying symptoms such as fever and chills.

Other typical signs include circulatory problems such as dizziness, headache, sore throat, body aches, nausea and vomiting.

As an acute allergic reaction of the skin to food or medication, the rash occurs as part of the so-called hives (also nettle fever). The increased release of the messenger histamine increases the permeability (permeability) of the blood vessels in the skin. The result is accumulation of fluid in the dermis, which leads to the formation of visible wheals combined with reddening of the skin and itching.

Hives can not only be caused by allergic reactions, but may also be the result of physical influences such as heat, cold, pressure, water contact or sun rays, whereby the symptoms are comparable to those of allergies.

Overall, the different accompanying symptoms and the efflorescence can provide important information about the causes of the rash and should therefore be taken into account accordingly in the diagnosis.

Diagnostics for itchy skin changes

The diagnosis is sometimes extremely complex due to the large number of possible triggers, but sometimes the cause of the complaints can be determined with a simple inspection. In the case of infectious diseases, the efflorescence in conjunction with the accompanying symptoms often already provides relatively reliable evidence for the diagnosis. A blood test for appropriate antibodies only serves to confirm the finding.

If there is a suspicion that an allergic reaction is causing the itchy rash, an appropriate allergy test can provide information. The extract of various allergens is applied to the skin as part of a so-called provocation test (prick test, intracutaneous test, scratch test) and the reaction is observed after a certain period of time.

Furthermore, blood tests can provide information about existing IgE antibodies (immunoglobulin E), which typically occur in allergic reactions. However, a distinction must be made here between increased IgE values ​​in the case of an allergy and the increased values ​​due to other diseases or parasites.

Fungal infections can usually be reliably diagnosed by laboratory examination of a microscopic smear. In many cases, however, the complexion already provides relatively reliable signs of the fungal disease. If it is suspected that the infection has also spread to the organs, a tissue sample must usually be taken for diagnosis. Ultrasound examinations, gastroscopy and computer tomography (CT) also offer possible assistance in diagnosis.

If parasite infestation is the cause of the symptoms, this can often be determined on the basis of the skin's appearance and microscopic examinations. With a special magnifying glass, the so-called dermatoscope, the bores of the mild can be identified, for example, in scabies. Sometimes the tiny arachnids are directly visible.

The microscopic examination of a skin sample from the affected areas serves to confirm the diagnosis. If you are suspected of cercariae, an examination of the bathing water can also be helpful in the diagnosis in addition to examining the skin. Checking the blood for antibodies against the larval components provides security here.

Since metabolic disorders such as diabetes and hyperthyroidism as well as liver diseases can lead to chronic itching, the presence of these symptoms should also be checked when making the diagnosis in case of doubt.

If it is not possible to determine the physical causes of the itchy rash, a psychological examination of those affected is advisable, since the skin irritation can also be due to psychological problems. In extensive discussions with the patients, the therapists try to identify possible mental complaints of those affected in order to derive methods that may be suitable for treatment.

Diagnosis of eczema and psoriasis

Neurodermatitis is diagnosed on the basis of various main and secondary criteria, with the itchy rash being one of the characteristic external features. The dry skin areas are also a typical symptom of atopic dermatitis.

However, since these skin problems can also occur in a large number of other diseases, differential diagnosis is of crucial importance. The itchy rash of atopic dermatitis must be differentiated from allergic skin reactions, metabolic diseases, diseases of the immune system, psoriasis and scabies.

The most important point of reference when diagnosing psoriasis is efflorescence. When scratching with a wooden spatula, light scales form on the affected areas, which in their consistency are reminiscent of candle wax. When peeling off the skin flakes, the last thin cuticle, which forms the border to the dermis, sometimes comes loose. Then punctiform bleeding can often be seen.

Both the candle wax-like scales as well as the peelable thin cuticle and the punctiform bleeding are considered typical signs of this form of skin lichen. Microscopic examination of skin samples taken can be used to confirm the diagnosis. Since many (skin) diseases resemble psoriasis in their appearance, differential diagnosis is also of particular importance for the skin disease.
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Continue reading:
Causes rash
Treatment for itchy rash

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Dipl. Geogr. Fabian Peters, Barbara Schindewolf-Lensch


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  • Dorothea Terhorst-Molawi: Dermatologie Basics, Elsevier / Urban Fischer Verlag, 4th edition, 2015
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Video: Eczema u0026 COVID-19: Managing itch (May 2022).