  
|  |
|
|
|
Written by Dr Virginia Hubbard, specialist registrar in dermatology and Dr Malcolm Rustin, consultant dermatologist
|
What is contact dermatitis?
Contact dermatitis is inflammation of the skin that results from
contact of an external substance with the skin. This can occur through one of
two mechanisms: irritant or allergic.
Irritant contact dermatitis
Irritants cause approximately 80 per cent of cases of contact
dermatitis. An irritant reaction is caused by the direct effect of an irritant
substance on the skin. An irritant substance is one that would cause an
inflammatory reaction in most individuals when applied in sufficient
concentration for an adequate amount of time.
Irritants are often encountered at work (occupational)
although other common irritants are soaps, detergents, food and cement. Almost
all workers in wet-work industries, such as hairdressing, cleaning, metal
engineering, building-site work and horticulture develop some degree of
irritant contact dermatitis.
Both sexes are equally susceptible to
irritant contact
dermatitis. Those with dry skins or who have one or more of the
'atopic' conditions (eczema,
asthma or
hay fever) are more
likely to develop an irritant contact dermatitis.
An irritant dermatitis is most likely to occur on the hands.
Allergic contact dermatitis
Allergic contact
dermatitis accounts for the remaining 20 per cent of cases. In this
condition, the cause of skin inflammation is a hypersensitivity reaction,
acting through the body's immune system, to a particular substance or
group of related substances.
Allergic contact dermatitis has the following
features:
-
previous exposure to the substance is needed to induce
allergy.
-
the reaction is specific to one chemical or a group of
similar chemicals.
-
all areas of skin that are in contact with the
allergy-provoking substance (allergen) develop the rash.
-
avoidance of the allergen will result in resolution of the
rash.
The commonest allergens are:
-
nickel
-
fragrances
-
rubber
-
some plants
-
formaldehyde
-
skin medications (including topical
corticosteroids)
-
hairdressing chemicals.
As with the irritant type, allergic contact dermatitis is more
common in atopic individuals.
What causes contact dermatitis?
Irritant contact dermatitis
Irritants cause direct injury to the skin. This can occur over
a short (acute) or long (chronic) period of time.
Acute irritant contact dermatitis
A single exposure to a substance causes an acute dermatitis,
within minutes to hours after exposure. The course of events is:
-
irritant substance penetrates the skin.
-
substance damages the membranes of skin cells.
-
cell damage prompts release of chemicals that trigger the
immune system into action. This is called an inflammatory response. The
chemicals involved (inflammatory mediators) include lysozymes, prostaglandins,
histamine and kinins.
-
some inflammatory mediators cause increased blood flow
while others attract further inflammatory mediators.
Chronic irritant contact dermatitis
This is due to multiple exposures, often to several
irritants at low levels over time. This dermatitis can take many months or
years to appear. The course of events is:
-
each exposure adds to the gradual disruption of the outer
layer of skin.
-
each time, inflammatory mediators are released.
-
the top layer of skin (epidermis) gradually
thickens.
-
the lipid (fat) layer in skin is gradually
damaged.
-
affected skin loses its ability to function as a barrier,
so further exposure to an irritant produces further damage, and a 'vicious
cycle' ensues.
-
the final result is dryness, scaling and thickening of the
skin.
Allergic contact dermatitis
This is a type of immune reaction known as 'type IV'
or 'delayed hypersensitivity' reaction. The characteristic feature of
this immune response is a delay between first exposure to an allergen and the
subsequent reaction. It, therefore, occurs in two stages, sensitisation and
elicitation.
Sensitisation phase
This starts with the substance penetrating the skin, which
then binds to Langerhans' cells (a type of skin immune cell), which then
leave the skin and travel to lymph nodes (glands) nearby. Here, the allergen is
shown to another type of immune cell, T-lymphocytes, which proliferate and
produce 'memory' cells that can remember that particular allergen.
Elicitation phase
Once sensitisation has occurred, subsequent exposure to the
allergen causes the T-lymphocytes to recognise the allergen, which activates
them and causes them to multiply. Inflammatory mediators are released that
induce the features of inflammation and bring more T-lymphocytes to the site of
exposure. This ongoing immune reaction results in the eczema-like inflammation
of the skin at the site of contact. This phase occurs within 48-72 hours after
exposure. Small amounts of allergen can be enough to cause an inflammatory
reaction.
What are the symptoms?
Irritant contact dermatitis
Acute
The appearance of acute irritant dermatitis can range from a
mild reaction consisting of transient redness to a severe painful burn with
blistering.
Chronic
Chronic irritant dermatitis often begins with a few patches
of dry, slightly inflamed skin that become thickened with time.
Allergic contact dermatitis
Early
The features of eczema develop at the site of contact. For
example, the first sign may be an itch under an earring or along a waistband
that contains rubber. The itch can develop into an area of redness with
swelling and even small blisters that weep.
In contrast to irritant contact dermatitis, the reaction can
extend beyond or occur in a different place from the site of contact.
Occasionally, the appearance is that of urticaria (severely itchy raised red
patches or wheals that can resemble insect bites, although these may be more
irregular in shape). Rarely, swelling of the mouth and upper airways can occur,
which is known as angioedema. This is serious and needs urgent medical
attention.
Prolonged
If exposure to an allergen persists, the skin becomes drier,
thicker and more scaly with a change in the pigmentation (colour).
How is contact dermatitis diagnosed?
The most important factor in making a diagnosis is the suspicion
by you or your doctor that a substance in your environment is causing the
dermatitis. Doctors should always think about the possibility of contact
dermatitis when managing a patient with an eczematous (eczema-like) reaction.
Two features are key to differentiating contact dermatitis from other causes of
an eczematous rash and to determine the offending substances: the timing of
onset or exacerbations and the part of the body that is affected.
Timing
Allergic contact dermatitis usually occurs 48 to 72 hours
after exposure, and will wax and wane depending on exposure.
Improvement of dermatitis during weekends or holidays is in
favour of an occupational origin for the offending substance.
Occurrence or worsening at weekends suggests a hobby or
environmental allergen.
Seasonal variation of dermatitis is seen in particular with
plant allergens, which can also be aggravated by light.
Body site
Contact dermatitis usually starts in and often remains
localised to the region most in contact with the offending substance. The
pattern of affected skin is a vital clue in the origin of the substance (eg, a
rash shaped exactly like your metal belt buckle could indicate an allergy to
nickel).
Location of contact dermatitis and suspicious agents
| Location |
Suspicious agent |
| Eyelids |
Eye makeup, airborne substances, nail polish |
| Earlobes or neck |
Metal jewellery |
| Forehead and hairline |
Hair dyes |
| Face |
Cosmetics (fragrance or preservatives), airborne
substances |
| Armpits |
Deodorants |
| Hands |
Gloves, occupational hazards |
| Waistband |
Elastic or nickel in belt or trouser stud |
| Feet |
Shoes - leather, plastic, glues |
All people who have an unusual dermatitis or one that resists
treatment should have
patch testing to test
whether certain contact allergens are aggravating the dermatitis.
What else could it be?
Several types of eczema-like reaction can produce a similar
appearance:
-
atopic eczema
-
seborrhoeic eczema (also know as seborrhoeic
dermatitis)
-
discoid eczema
-
pompholyx (small water blisters on the hands and
feet)
-
stasis or venous eczema
-
asteatotic eczema.
Confusingly, any of the above conditions can be exacerbated by
an allergic or irritant component.
Other skin conditions that should be considered are:
-
drug eruption - usually suggested by a history of a rash that
occurs after starting a new drug treatment.
-
fungal infection - scrapings of the skin can be taken and
examined under a microscope to make the diagnosis.
What can you do?
Prevention
-
Use gloves and protective clothing when dealing with
potentially irritant substances (even for repeated or prolonged exposure to
water).
-
Thoroughly clean your skin if you come in contact with
potential irritants.
Determine the cause
-
Make a list of substances that come in contact with your
skin.
-
Record the timing of use of each substance and see if it
relates to the timing of your dermatitis.
-
Record the body area exposed to each substance and see if it
relates to the site of your dermatitis.
Treatment
-
Avoid the suspected irritant or allergen. This is sometimes
not possible but use of protective clothing, such as gloves, can help. In some
cases of occupational exposure, time away from work may be
necessary.
What can your doctor do?
Once the diagnosis is made, and suspicious substances have been
identified, your doctor will advise you how to avoid the suspected/offending
substance.
Avoidance often resolves the dermatitis but if this is difficult
or if the dermatitis is long standing, you will need drug treatments.
Corticosteroids in the form of creams and ointments can be applied to the
affected area to reduce the inflammation.
Antihistamine
treatments can sometimes help with redness and itching, particularly
with urticaria.
What can your dermatologist do?
For some patients, a referral to a skin specialist
(dermatologist) is needed. The dermatologist will:
-
discuss possible offending substances.
-
offer patch testing to
check for allergies. Suspected allergens, including a battery of standard
allergens, are applied usually to the back under aluminium discs or patches.
These are left in place for 48 hours and then removed and the skin inspected.
After a further 48 hours, the sites are inspected again. Reactions can range
from mild redness to severe painful blistering. The results of the patch tests
are then interpreted in the light of the history and possible previous exposure
to the allergen.
-
discuss sources of the irritant or allergen and the relevance
to you. Often an information sheet will be given.
-
suggest ways of avoiding contact with the substance.
-
suggest how to minimise exposure if avoidance is not possible,
using:
-
protective clothing
-
barrier creams (the use of barrier creams is
controversial). Their efficacy varies depending on the constituents of the
cream and the specific irritant. In general, barrier creams are a poor
substitute for gloves. However, their use reminds both the employer and
employee about the potential link between their job and dermatitis.
-
Discuss how a slight change in your work pattern may help. For
example, a hairdresser with contact allergy to a constituent of permanent hair
dye could avoid colouring and concentrate on cutting instead. A letter from
your dermatologist to your employer may help. Sometimes a change in career
needs to be considered.
-
Advise on suitable treatment in case of active dermatitis:
-
suitable
moisturisers
-
topical
corticosteroids, which suppress the inflammatory reaction so should
reduce redness, swelling and pain.
What is the outlook?
Whether the dermatitis will settle or recur depends on several
factors.
-
Can the cause be avoided? If it can, the dermatitis will
usually settle within a week. If the irritant or allergen is widespread, eg
nickel found in jewellery, studs, coins and keys, then minimising exposure will
help prevent recurrence. In some severe cases, a change in career should be
considered.
-
Does the patient also have
atopic eczema? If so,
then the risk is higher for developing a contact dermatitis.
-
Body site affected. Hand contact dermatitis is often the result
of several irritants and allergens and is more difficult to manage.
-
Speed of recovery of the barrier function of the
skin.
-
Superimposed infection can prolong dermatitis.
-
Treatments used can themselves act as irritants or allergens
and delay recovery. This can occur with topical antibacterial creams, the
constituents of medicated bandages or with herbal remedies.
|
References
Belsito DV. The diagnostic evaluation, treatment, and
prevention of allergic contact dermatitis in the new millenium. J Allergy Clin
Immunol 2000 Mar; 105(3): 409-20.
Leow YH. Contact dermatitis due to topical traditional
Chinese herbal medication. Clinics in Dermatology 1997 Jul-Aug; 15(4):
601-05.
Mowad CM. Update on contact dermatitis. Advances in
Dermatology 1999; 14: 61-86.
|
|
Last updated 01.08.2005
|
 |
|
|
 |
| |      |
|
