Contact Allergic DermatitisContact allergic dermatitis due to eyedrop preservatives
What is contact allergic dermatitis?
Contact allergic dermatitis (contact
dermatitis) develops after skin contact with external "allergens".
A red, itchy and often blistering weeping rash develops, typically
within a few days of contact with external "allergens".
Timing is everything
Skin irritation, itch and redness may
start within half to 5 days after exposure, but the average is
2 to 3 days. The rash then worsen over the next 2 to 3 days, and
watery blisters are often noticed. Symptoms then settle over a
period of 3 to 7 days, with involved skin becoming dry and rough,
and often peeling.
What is happening?
The body's immune system recognizes
allergen as "foreign". When this happens, white cells
are attracted from the blood into the skin over several days.
This results in inflammation and the development of a rash.
Common causes
Over 2000 contact allergens have been
identified, of which nickel, plants and perfumes are the most
common. Here are some of many:
NICKEL DERMATITIS. Around 1 % of the population is allergic to
this metal, present in plated jewellery, watch buckles, jeans
studs, keys, coins, bra clips, cooking utensils, gym equipment.
HAIR DYES.
RUBBER ADDITIVES. eg. gloves, rubber handled tools or gym equipment
or bike handles.
FRAGRANCES. eg. perfume, shampoos, cosmetics, tissues, deodorants,
domestic cleaners.
LEATHER ADDITIVES, TEXTILE DYES
FORMALDEHYDE. eg. permanent press clothes, cosmetic preservatives,
glossy paper
COLOPHONY. This is a pine resin present in wood as well as pine
oil cleaners and band aid gums
PLANTS. eg. grevillea, bulbs, daisies, dandelions, chrysanthemum,
ivy, tomato plants, zucchini plants, garlic, onion, primrose,
poison ivy, mango (often causes a rash around the mouth), Rhus
trees, tea tree oil
COSMETICS / SUNSCREEN ADDITIVES. eg. PABA, oxybenzone, benzophenone
PLASTICS. eg methacrylates glues, dental plates and even Australian
plastic bank notes!.
FLAVOURING AGENTS. eg. cinnamates in toothpastes or foods.
MEDICATION PRESERVATIVES. eg. benzylkonium chloride in eyedrops,
lanolin in some creams, topical antibiotics or local anaesthetics
(used to treat sting/bite reactions).
Contact
dermatitis due to cosmetic sensitivity (left) and plants (right)
Nickel dermatitis from contact with
jeans studs (left) and necklace (right)
Nickel
dermatitis from contact with nickel plated paint spray gun.
Hand
dermatitis from sticking plaster (left) and shoes (right).
Sometimes light is needed too
So-called photo-contact dermatitis
requires both contact with allergen and light exposure for a rash
to develop.
The story is everything
Because the rash does not develop immediately,
the story surrounding the episode is very important. This will
help you and your doctor to identify the cause so that exposure
can be avoided in the future. You may be asked to write down what
you have done or come into contact with, in the previous few
days.
When to suspect contact allergic dermatitis?
While there are no firm rules, one
must be suspicious in some circumstances such as isolated face
or eyelid dermatitis, hand dermatitis or the sudden onset of dermatitis
in someone who has not had similar rashes before. Rashes involving
only 1 or 2 body areas may also lead one to suspect a localized
allergic cause.
Obvious contact with allergen is not always
needed
Contact with airborne plant-derived
allergen can also cause dermatitis. This is commonly known as
"Australian bush dermatitis", ragweed dermatitis or
weed dermatitis. Wind-blown allergen comes into contact with exposed
areas of skin over the face, eyelids, sides of neck and "V"
area of the neck and upper chest. Dermatitis often occurs after
being outside on a windy days in the warmer months of the year.
There is usually a sharp line between affected areas, and normal
skin protected by clothing. Even lightly brushing past a plant
can trigger dermatitis in someone very sensitive to it.
Allergy testing (Patch testing)
Skin prick testing is of no use in
this condition. Instead, "Patch testing" is performed.
Commercial allergen extracts are applied to marked areas of rash-free
skin, usually over the back. Allergen extracts are applied using
low allergen tape.and left in place for around 2 days. The results
are then "read" over the next few days. The presence
of a rash under an individual allergen indicates sensitivity to
this substance. This does not prove that this particular allergen
is the cause, but may provide a clue of what may be causing your
problem.
Left to right: Patch test allergens; Patch tests on the back; Patch test results.
How is contact dermatitis treated?
Antihistamines (such as Claratyne,
Telfast, Zyrtec, Phenergan or Polaramine) are usually unhelpful
in controlling itch or irritation. Mild rashes can be treated
with cortisone / steroid creams to reduce inflammation. Severe
blistering episodes usually require cortisone / steroid tablets
for several days to control symptoms.
References
