Contact dermatitis is an eczematous disease caused by exposure to substances
in the environment. Clinical presentation of contact dermatitis, which
has characteristic distribution patterns, is a critical guide in the diagnosis
of the disease. These patterns help, firstly, in diagnosing whether the
condition is due to external or internal reasons and secondly in detecting
the offending agent.
Clinical presentation shape and location
The shape and site of the inflammation is often an important clue to
the identity of the allergen. Inflammation on the scalp and ears may be
due to shampoo, hair dyes and topical medications among others and facial
inflammation may be caused by cosmetics, acne medications and air-borne
allergens, like ragweed. Sometimes the shape and location of the inflammation
is exactly the same as the shape of the offending object. Therefore, the
offending agent is easily identified when the inflammation appears restricted
to the area under the objects, such as, a watch strap, shoes, or other
clothing articles. Cotnact with allergen inducing plants like poison ivy
produce linear patterns of inflammation.
But most inflammation in contact dermatitis is not confined to the area
in contact with the allergen. If the allergen is present in a cosmetic
or any facial make-up, then the rash is often patchy rather than diffuse
and spread over all the facial areas where the cosmetic was applied. Allergens
may also spread, accidentally, to areas where they were not meant to be
applied. For example, hair dyes may spread to the ears and face. The scalp,
palms and soles of the feet are more resistant to contact dermatitis,
since the skin is thicker at these sites. But affected individuals may
develop minimal inflammation if the adjacent areas of skin are affected.
Aeroallergens (in the air) affect only the exposed areas of the skin and
spare areas covered by clothing.
Recent studies show that contact dermatitis produced by clothing allergens
are not that rare as was earlier thought. Textile contact dermatitis produces
clinical patterns which are similar to patterns occurring in other types
of contact dermatitis, but also produce patterns that are unusual and
located at unusual places, such as, shins and inner thighs. The inflammation
is sometimes pruritic. Diagnosis of such cases presents special problems
to a doctor and a correct diagnosis can be difficult.
Intensity and patterns
The inflammation intensity and pattern depends on the degree of sensitivity
of the person and the concentration of the allergen. Allergens which are
strong sensitizers, like, oleoresin of poison ivy plants, can produce
intense inflammation in low concentrations, whereas weak sensitizers may
produce only erythema. The clinical presentation also depends on the area
of skin affected and duration of exposure to the allergen.
Acute inflammation shows macular erythema, edema and vesicles, while
chronic inflammation features lichenification, scaling and fissures in
the skin. Contact dermatitis may also exhibit non-eczematous characteristics,
such as, cellular-like appearance of dermal contact hypersensitivity,
lichenoid variants and contact leukoderma.
Direct versus air-borne contact
Acute and chronic contact dermatitis of exposed parts of the body, particularly
the face, may be due to chemicals in the environment, such as, sprays,
perfumes, chemical dusts and plant pollen, especially ragweed pollen.
The air-borne allergens tend to produce inflammation which is more diffuse
and. Air-borne allergens collect easily on the upper eyelids, and the
eyelid skin is particularly vulnerable to dermatitis because it is relatively
thin. Photo dermatitis also has a diffused distribution of the rashes
it causes. Volatile substances can collect in clothing.
Clinical presentation of rhus contact dermatitis
A type of contact dermatitis, known as rhus dermatitis, outnumbers, in
its incidence, all other types of contact dermatitis in the USA. It is
caused by contact with the substance oleoresin present in the plant poison
ivy and those belonging to the same family, such as, mango trees and cashew
trees. All parts of these plants contain oleoresin.
The contact dermatitis occurs when the skin contacts the leaf or internal
parts of the root or stem. The clinical presentation depends on the quantity
of oleoresin contacted, the pattern in which the contact was made, susceptibility
of the skin and regional variations in skin reactivity. Large amounts
of oleoresins cause intense inflammation whereas small amounts produce
only mild skin erythema (redness).
The linear patterns of inflammation that is very typical of rhus dermatitis,
is produced when a plant part is drawn across the skin or from streaking
the oleoresin while scratching the itchy skin.
Diffuse or unusual patterns of inflammation are produced when the oleoresin
is contacted from contaminated animal hair or clothing or from smoke while
burning the plant. The eruption may appear in as quickly as 8 hours after
contact or may appear a week or more later. The appearance of new lesions
a week after contact may be confusing to the patient, who may attribute
new lesions to the spread of the disease by touching active lesions or
to contamination with blister fluid. Blister fluid does not contain the
oleoresin and, contrary to popular belief, cannot spread the inflammation.