Encyclopedia of Health and Medicine

allergic dermatitis 241
EYE irritation that interferes with
vision, causes PAIN, or follows injury to
the eye requires a doctor’s prompt evaluation.
The most common form of allergic conjunctivitis
develops seasonally when airborne pollens are
high. Some people develop allergic conjunctivitis
with exposure to allergens such as dust and pet
dander (especially cat dander) as part of a broader
ALLERGY picture. People who have seasonal allergies
(ALLERGIC RHINITIS), ALLERGIC ASTHMA, or other
ATOPY conditions may have a GENETIC PREDISPOSITION
for type I hypersensitivity reactions that puts them
at higher risk for developing allergic conjunctivitis
as well.
Treatment for allergic conjunctivitis combines
avoiding the responsible ALLERGEN with EYE drops
that contain an antihistamine or, for severe symptoms,
a corticosteroid (anti-inflammatory medication
that suppresses the IMMUNE RESPONSE).
ANTIHISTAMINE MEDICATIONS neutralize the histamine
responsible for the allergic response. Systemic
antihistamine medications (allergy relief products)
may also help, especially when there are accompanying
allergy symptoms such as allergic rhinitis.
Natural tears eye drops can restore moisture to
eyes that are scratchy and dry. Allergic conjunctivitis
generally resolves when exposure to the
allergen ends, which may be the end of allergy
season when seasonal allergies (hay fever) are
responsible.
See also ALLERGIC DERMATITIS; DRY EYE SYNDROME;
INFECTION; LIVING WITH ALLERGIES.
allergic dermatitis A HYPERSENSITIVITY REACTION
(allergic reaction) that affects the SKIN, usually in
response to contact with an ALLERGEN. As with all
hypersensitivity reactions, the first exposure to the
allergen produces no symptoms. In reaction to the
exposure, however, the IMMUNE SYSTEM produces
antibodies for the allergen. Subsequent exposures
to the allergen then do produce symptoms. Abundant
immune cells reside in the epidermis, the
inner layer of skin that contains living cells, to
react to the allergen.
Most allergic dermatitis is a type IV, or delayed,
hypersensitivity reaction. Symptoms generally
affect only the area of contact and begin to emerge
24 to 36 hours after the contact, though may start
within hours to a week later. Sometimes there can
be repeated exposure before the hypersensitivity
reaction occurs, though most commonly the second
exposure triggers the ALLERGY.
A less common but more severe form of reaction
is atopic dermatitis, a chronic type I
(IMMUNOGLOBULIN E [IgE]) hypersensitivity reaction.
Atopic DERMATITIS, commonly called eczema,
tends to occur in people who have other chronic
hypersensitivity conditions such as ALLERGIC
ASTHMA and ALLERGIC RHINITIS. GENETIC PREDISPOSI-
TION is the most significant risk factor for atopic
dermatitis. Often there is no apparent contact
allergen that sets off an atopic dermatitis attack,
and symptoms may continue for several weeks to
months or appear to never quite go away.
POISON IVY, POISON OAK, AND POISON SUMAC
The blistering, itchy RASH that some people
develop with exposure to poison ivy, poison oak,
and poison sumac is an allergic reaction to the
resins on the surface of these plants. Repeated
contact creates as well as intensifies sensitivity.
In a highly allergic person, a reaction may occur
through contact with clothing that came into
contact with the resins. Contrary to popular
belief, the fluid in the rash’s blisters does not
spread the irritation. The rash appears to spread
because the person’s sensitivity to the resin
increases even as the allergic reaction unfolds.
Symptoms and Diagnostic Path
Allergic dermatitis, sometimes called allergic contact
dermatitis, results in URTICARIA (hives) or RASH,
often along with itching. BLISTER formation is common.
The diagnosis is fairly straightforward when
the person knows he or she has had contact with
a known allergen. It is sometimes difficult to distinguish
allergic dermatitis from other forms of
dermatitis. In such situations ALLERGY TESTING, in
which the allergist places small amounts of suspect
substances in patches on the skin, can often determine
the responsible allergen. Many substances,
such as detergents and cleaning chemicals, can
cause contact dermatitis through direct damage to
the cells of the skin. Though symptoms are similar
to those of allergic dermatitis, the irritation occurs