From measles and chickenpox to urticaria: understanding what skin rashes can reveal about our health

If someone asks you, “Did you have chickenpox as a child?”, the answer is usually “Yes”. However, if they ask for clarification — “Was it really chickenpox, or could it have been scarlet fever, measles or fifth disease?” — the answer is often, somewhat embarrassed: “I think it was chickenpox.”

In fact, there are several exanthematous diseases — those that cause red spots and rashes, to put it simply — that can easily be confused with one another. Some are considered childhood diseases, such as those mentioned above. However, the list is very long, and distinguishing between them is not always easy.

The aim of this article is therefore not to turn the reader into a specialist in these diseases, but rather to raise awareness of their possible origins and consequences.

A story of small red spots

What is an exanthematous disease? It is a disease, most often of infectious origin, characterised by the appearance of a skin rash, sometimes accompanied by other symptoms such as fever, fatigue or respiratory problems.

There are many possible causes. These include infections, allergies such as urticaria, autoimmune diseases and drug-induced reactions.

Why do exanthems appear? These small red spots are the result of a three-stage inflammatory cascade. Initially, there is an antigen, such as an infection or autoimmune disease, an allergen or a toxin, such as a drug. This is followed by an immune cascade that causes an inflammatory reaction in the skin.

Since the final visible result of these conditions can be very similar, identifying their origin requires consideration of all symptoms, the patient’s medical history and that of the people around them. This is the role of the family doctor, enabling them to choose the most appropriate treatment.

Infectious exanthems: different in children and adults

Infectious exanthems do not present in the same way across different age groups. In children, they are often associated with well-known viral infections and follow fairly typical patterns. This is the case for diseases such as measles, chickenpox and rubella.

The rash is generally recognisable and evolves in a relatively predictable way, often remaining benign in healthy children.

In adults, the situation is different. Infectious exanthems are less common and, above all, much more variable. They may be caused by many different viruses and bacteria. The rash is often less typical and sometimes misleading, making diagnosis more complex.

In adults, a simple skin rash may therefore reveal a more widespread or more serious infection, requiring careful medical assessment.

And when infection is not the cause…

Not all skin rashes are caused by microbes, and this changes the diagnostic approach. In these cases, the body is reacting to something else: a medicine, an allergen or a disorder of the immune system.

This is particularly true of urticaria, where the skin reacts rapidly, with red wheals appearing and sometimes disappearing within a few hours.

The role of the laboratory in diagnosis

The laboratory plays a crucial role in the diagnosis of exanthematous diseases, especially when the appearance of the rash alone is not enough to identify the cause.

Through tests such as PCR or serology, it can confirm an infectious origin, for example in diseases such as measles or Parvovirus B19 infection, and distinguish these from non-infectious causes such as urticaria.

Laboratory testing therefore helps establish an accurate diagnosis, personalise patient care and, when necessary, implement preventive measures to limit the spread of certain diseases.

Exanthematous diseases: some illustrative examples

Measles: a current public health issue

Measles is an extremely contagious disease. One infected person can infect 12 to 18 unvaccinated people, making it one of the most transmissible infectious diseases.

In addition, people are already contagious several days before the rash appears, which facilitates silent spread.

Measles remains a global health concern, causing around 100,000 deaths each year worldwide, mainly among unvaccinated children. Europe also recorded a sharp increase in cases and deaths in 2024.

Measles control relies on very high vaccination coverage. To stop the circulation of the virus, 95% of the population must be immunised with two doses of vaccine. In Ticino, we are almost there; in other cantons, slightly less so.

Rubella: when a simple rash threatens the fetus

Rubella is a viral rash illness that is generally mild in children and adults, but can have serious effects on the fetus when infection occurs during pregnancy.

Major epidemics led to the identification of congenital rubella syndrome, associated with deafness, eye damage and heart defects.

The introduction of vaccination has led to a significant decrease in virus circulation and cases of congenital rubella syndrome in countries with high vaccination coverage.

Varicella-zoster virus: two diseases in one

The varicella-zoster virus is unique: it first causes chickenpox and can then remain latent in the body.

Years later, it may reactivate and cause shingles, which is often painful. Chickenpox and shingles are therefore two manifestations of the same virus.

Urticaria: a rapid and visible reaction

Urticaria is a common reaction, often linked to an allergy. Wheals appear quickly, change location and may disappear within a few hours.

Although impressive, they are generally benign and clearly illustrate the skin’s ability to react immediately to an internal imbalance.

The skin tells a story

Understanding a skin rash does not simply mean recognising it, but also identifying its origin: infectious or not, typical or atypical, benign or more concerning.

This reasoning transforms a simple skin sign into a real key to understanding a person’s state of health. The doctor looks for clues — how the lesions evolve, associated symptoms and the clinical context — and every detail matters. A recent trip or contact with a sick child, for example, may be useful for diagnosis.

Exanthematous diseases are therefore not simply “spots” or “pimples”. They form a true language of the body, where each rash is a message to be decoded.

Author: Dr Giuseppe Togni