dermatitis
Meaning of dermatitis: Where a rash sits is often the strongest clue to its cause, since contact reactions trace the outline of whatever touched the skin.
Definition of dermatitis
Dermatitis means inflammation of the skin. It is a description rather than a single diagnosis, covering any process that leaves skin red, swollen, itchy, dry, scaling, weeping or cracked. Pattern, location and timing usually reveal more about the cause than the appearance of the rash alone, which is why the word is nearly always qualified with a specific type.
What are the main types?
| Type | Trigger | Typical pattern |
|---|---|---|
| Irritant contact | Direct chemical or physical damage; no immune memory needed | Hands of people who wash or handle solvents repeatedly |
| Allergic contact | Immune reaction to a substance after previous sensitization | Shaped exactly like the object: a watch strap, a nickel button |
| Atopic | Barrier defect plus immune overactivity, often with asthma or hay fever | Elbow and knee creases, neck, face in infants |
| Seborrheic | Reaction to a normal skin yeast in oily areas | Scalp, eyebrows, sides of the nose |
| Stasis | Long-standing venous congestion in the legs | Both lower legs, with staining and swelling |
What separates irritant from allergic contact dermatitis?
Both follow contact, but the mechanism differs and so does the timing. An irritant reaction is dose-dependent damage that can affect anyone given enough exposure, and it appears within hours. An allergic reaction requires a previous encounter that taught the immune system to recognize the allergen, then appears a day or two after the next exposure, and a trivial amount is enough. Patch testing distinguishes them by applying suspected substances to the back under discs and reading the skin after a set interval. Nickel, fragrance mixes, preservatives and rubber chemicals are among the most frequent culprits.
How is the cause narrowed down?
History carries most of the weight: occupation, hobbies, cosmetics, new medications and whether the rash improves during time away from work. Distribution is read carefully, since inflammation confined to sun-exposed areas suggests a photosensitive reaction, while a rash sparing skin under a watch or a ring points elsewhere. A skin biopsy is used mainly to exclude look-alike conditions rather than to name the type. Treatment fields have their own entries, such as radiation dermatitis, where the trigger is already known.
Also known as
Used in a sentence
The patient developed dermatitis on the hands after repeated exposure to the cleaning solution.
Good to know
Dermatitis describes a pattern of skin inflammation rather than a single disease, so the term is typically qualified with a more specific type, such as contact or atopic dermatitis, to convey the underlying cause.
Word origin
Where “dermatitis” comes from
Formed from dermat-, from Greek derma, meaning skin, combined with -itis, meaning inflammation.