Rash

Rash: The Language of the Skin

A rash (exanthem) is any pathological change on the skin characterized by a change in its colour, texture, or the appearance of elements such as macules, papules, vesicles, or pustules. It is not a disease in itself but an extremely common symptom that can indicate a wide range of conditions: from simple irritation to serious systemic illnesses. For a dermatologist, a rash is the language through which the skin communicates internal and external problems. Analyzing the rash’s characteristics, distribution, and accompanying symptoms is key to diagnosis.

Rash Morphology: How Elements Are Described

To describe a rash, clinicians use specific terms for its various elements:

• Macule (spot): A change in skin colour without alteration of its surface (e.g., freckles).
• Papule (nodule): An element that rises above the skin surface without a cavity inside.
• Vesicle (blister): A small elevation above the skin filled with clear fluid (e.g., in chickenpox).
• Pustule (pus-filled blister): An elevation filled with pus.
• Urticaria (hive): An element in hives that arises due to skin swelling.

Causes of Rash: From Infections to Allergies

The causes of rash can be broadly divided into several major groups:

• Infectious:
  • Viral: Measles, rubella, chickenpox, infectious erythema, roseola. The rash in these conditions is often accompanied by fever.
  • Bacterial: Scarlet fever, impetigo.
  • Fungal: Dermatophytoses ("ringworm").
• Allergic: Hives, atopic dermatitis (eczema), contact dermatitis. These allergic reactions are usually accompanied by intense itching.
• Autoimmune: Psoriasis, systemic lupus erythematosus.

A rash can also be a reaction to burns, insect bites, or irritation. Rash in children is described in detail in the article "Rash in Children".