Allergic Skin Diseases

Tony is an 8 year old atopic; who has been labelled as "egg anaphylactic" since age 2. He suffered infantile eczema, but now only gets perennial rhinitis with infrequent mild asthma. He started getting recurrent episodes of skin rashes at the age of 4.

The rashes were always acute in onset, and varied between localised redness, with burning to generalised erythema and sometimes blisters. Some of the episodes were attributed to inadvertent egg contact and treated as acute contact urticaria or anaphylaxis with antihistamines, with poor response. However, these were never proven. The worse episode occurred the day after attending a bonfire and caused generalised erythema with angioedema of his face, with gross peri-orbital edema causing inability to open his eyes. He was admitted to hospital overnight and treated with intravenous hydrocortisone and discharged on oral prednisone. A patch test done 1 month after this episode showed very strong positive reaction to compositae mix, colophony and fragrance mix. This confirmed the cause of the recurrent skin rashes as allergic contact dermatitis to these allergens. The reaction following the bonfire was thought to be due to burnt compositae or poison ivy fumes.

This case highlights several important points about recurrent skin rashes:

  • Acute Allergic Contact Dermatitis can masquerade as anaphylaxis (to the non-expert).
  • If an acute skin rash is poorly responsive to antihistamines, acute urticaria is less likely than allergic contact dermatitis.
  • Blisters are not typical features of contact urticaria, and are more likely in acute contact dermatitis.
  • Atopic Eczema, Allergic Contact Dermatitis and Acute Urticaria (Hives) should always be considered in recurrent skin rashes.
  • Allergic Contact Dermatitis (ACD) is not uncommon in children, as is the view held by some medical practitioners.
  • Allergic contact dermatitis is no less common in atopics, than non-atopics (again another myth).
  • A patch test should be considered in all recurrent, undiagnosed skin rashes.
  • Patients with atopic eczema often have allergic contact dermatitis as well.

There are 3 major skin diseases caused by allergies:
1. Eczema
2. Allergic Contact Dermatitis
3. Hives (Acute Urticaria)

It is important to remember that any combination of the 3 can occur in the same patient at the same or different times.

1. Eczema

Eczema is a common allergic skin disease in infants. It usually develops around 4 months of age. In some cases the term eczema is used interchangeably with dermatitis. Some prefer to reserve the term dermatitis, for cases of eczema caused by an external trigger, as in the case of allergic contact dermatitis.

In most cases, eczema resolves itself in infancy or at least by the time the child is 5 years old. It is usually the first symptom of the allergic march, often to be followed by asthma or hay fever, as seen in atopics.
The symptom that occurs almost invariably in eczema is itching (pruritus). If this symptom is not present, the diagnosis of eczema should be seriously questioned.

There are two forms of eczema. Acute eczema causes red, swollen patches on the skin, with watery discharge (oozing), and usually causes severe discomfort. Chronic eczema causes thickened, scaly skin patches, which often gets secondarily infected leading to crusting. As the term implies, chronic eczema tends to last, sometimes for years and in rare cases for life.

In infants, eczema usually appears on the cheeks, scalp, neck and trunk. In children over two years old, eczema usually appears in the knee and elbow creases, the neck, wrists and ankles. However, there is overlap between the age groups, and other areas of the body may be involved.

Factors affecting Eczema

The exact cause of eczema is unknown, but we do know some of the factors that precipitate or aggravate it. The main factor is heredity. About one-third of children with eczema have parents or close relatives who have eczema, asthma or hay fever (are atopic). Several studies have shown that, foods like milk, eggs, wheat, peanuts and soy are common causes of eczema in infancy. It is advisable to skin test all infants with severe eczema to these foods.

Skin irritants, such as soaps, detergents and wool can all aggravate eczema.

Climate can also trigger eczema. Babies who are brought from warm countries to areas where the climate is cold are particularly vulnerable. Cold, dry air causes the skin to become dry and itchy. A hot, humid climate can also cause sweating, which worsens the itching and scratching in eczema.

2. Allergic Contact Dermatitis

This form of allergic skin disease occurs when a substance that comes in direct contact with the skin causes an eczematous reaction. It is usually impossible to tell the difference between atopic eczema and allergic contact dermatitis purely by examination of the rash. A thorough history and a suspicious, detective's mind is the most useful tool in helping to differentiate the two.

Poison Ivy is one of the most common and familiar causes of contact dermatitis. Other leaves such as oak and sumac can also cause contact dermatitis. The resin in the leaves is the offending agent.

Since new potentially sensitising chemicals are continually coming into use, the prevalence of allergic contact dermatitis will only continue to increase.

Contact dermatitis is the most common occupational disease, and as such, it is of tremendous importance to both the individual and society.

Allergic contact dermatitis may appear at any age. It is increasingly being looked for and recognised in childhood. It is probably equally common in the general and atopic populations, and a history of concomitant or family allergy is of no help. Sensitivity to nickel is approximately 10% in women.

The interval between exposure to the causative agent and the manifestations of symptoms is usually 12 to 48 hours (A Delayed hypersensitivity reaction). The incubation period (ie. the time between initial exposure to the agent and the development of skin sensitivity) may be as short as 2 or 3 days in the case of strong sensitisers such as poison ivy, or as long as several years for a weak sensitiser such as chromate. Once sensitivity is established, it generally persists for many years (sometimes indefinitely).

The clinical appearance of allergic contact dermatitis depends upon the stage at which the patient presents. In the acute stage, redness, bumps and blisters predominate. Swelling of the eyelids is common when the face is affected. This can be mistaken for angioedema seen in acute allergic reactions associated with hives, as seen in food and drug allergy. In the chronic stage few bumps or blisters are seen, and thickening and scaling predominate.

Skin areas vary in their susceptibility to sensitisation by contact allergens. The eyelids, neck, and genitalia are amongst the most easily sensitised areas. The palms, soles and scalp are more resistant, since the skin is thicker. Pressure, friction and perspiration seems to promote the process of sensitisation, and a tissue that is already irritated, inflamed, or infected has heightened susceptibility.

Often the location of the dermatitis is the place at which the patient's skin surface made direct contact with the allergen.

Salient Features of the rash in Allergic Contact Dermatitis:

  • It is usually slow to start, and can be delayed up to 4 days after first contact.
  • It is usually prolonged, lasting 7-10 days after a single contact.
  • It can be started by contact with only minute amounts of the allergenic substance.
  • It may spread to cause a rash outside the area of contact, sometimes all over the body.

The diagnosis of Allergic Contact dermatitis is confirmed by doing a Patch Test .

Patch Testing – Patient Instruction Sheet

We believe that your skin disease may be related to contact with chemicals in your environment. This is called allergic contact dermatitis.

The only way to obtain proof of allergic contact dermatitis is by patch testing. This is different from skin prick testing (which gives a positive response in 15 minutes) in that it is a delayed hypersensitivity response (positive response in about 48 hours).

Chemicals will be taped to your back in small chambers. The skin will not be broken. The "patches" stay in place for 48 hours. You cannot shower or do any work or exercise that will wet or loosen the patches.
The "patches" will be removed, and a reading will be done after 2 days. The patch sites will be marked, and you may be asked to return for a final reading on another day. Between the two readings you can bathe, but you may not wash your back.

You may develop itching under the patches. If it becomes very severe or if you develop pain, you should contact the clinic. If you are unable to contact the clinic, have someone carefully remove the painful patch. Try not to disturb the other patches.

You may develop blisters at the positive sites, and very rarely prolonged reactions or even scars may develop at such sites.

You will be tested for your response to common chemicals. If you believe that any agent or product even a medication worsen your problem, please bring it with you (and the container with the ingredient list) when you come for patch testing.

You should not be tested if you are taking cortisone pills (eg. prednisone), have had a cortisone injection, are applying cortisone to your back, or have had sun on your back recently. Please tell the nurse or doctor if any of these have occurred. Please tell the doctor if you are pregnant. Please call if you have any problems. Please ask if you have any questions.

Your tests may be completely negative. This probably means that a contact allergy is not the cause of your skin problem. The test is not infallible, however, and an allergy may be missed. Retesting in the future may be indicated.

Allergens tested in the Standard Patch Test:

  • Potassium Dichromate
  • Neomycin Sulphate
  • Thiuram mix
  • Paraphenylendiamine
  • Cobalt Chloride
  • Benzocaine
  • Formaldehyde
  • Colophony
  • Clioquinol
  • Balsam of Peru
  • N-Isopropyl-N-Phenyl parapheylendiamine
  • Wool alcohols- Lanolin
  • Mercapto mix
  • Epoxy resin
  • Paraben mix
  • Partertiarybutyl-Phenol Formaldehyde Resin
  • Fragrance mix
  • Quaternium
  • Nickel Sulphate
  • 5-chloro-2-methyl-4-isothiazolin
  • Mercaptobenzothiazole
  • Sesquiterpene lactone mix
  • Primin
  • Alpha-amyl-chinnamaldehyde
  • Compositae Mix

3. Hives (Acute Urticaria)

Hives are itchy skin rashes with raised weals of different sizes. Sometimes they look like mosquito bites. They are sometimes referred to as urticaria. They may appear a few at a time or they may spread over the whole body. Hives tend to come and go and change places over the body. They last from minutes to days or may recur in crops for a period of weeks or months in different areas. If hives last for more than six weeks they are called chronic urticaria. Hives lasting less than six weeks are known as acute urticaria.
Hives may affect the deeper layers of the skin and cause swelling. This is called angioedema. Hives and angioedema may appear together or separately.

Hives can be caused by foods (especially milk, eggs, wheat, seafood, & peanuts), drugs like aspirin and penicillin, infections and inhaled substances like cat hair and house dust mites. Physical agents like cold, heat, sunlight, direct pressure, vibration and rubbing can also cause hives in some people. Insects like mosquitos, bed bugs and fleas can produce small crops of small itchy swellings on exposed parts of the body, especially the lower extremities in children. These may be a form of hives called papular urticaria.

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