ABC of Safety in the Biological Sciences




An allergy is an abnormal and individual hypersensitivity to any substance that is ordinarily harmless and is acquired by exposure to that particular allergen.33

Many substances used in the histopathology laboratory are potential allergens (see Allergen, this section). If an allergic reaction develops the allergen needs to be identified so that, if necessary, the particular person can avoid or modify their use of the material. It may become necessary to remove an affected person entirely from an area where a particular allergen causes them concern.

Allergy related disorders encountered in laboratory personnel include the following:

Eczema (contact dermatitis)
Contact dermatitis may be caused by primary contact with an allergen or there may be a delayed hypersensitivity. The allergens concerned are usually highly reactive chemical compounds capable of combining with proteins and also dissolving in lipids thus allowing for penetration of the dermis. Some reactions occur from repeated contact with a substance over many months. Direct irritants may damage normal skin or irritate an existing dermatitis. Weak or marginal irritants such as soap, acetone or even water may take several days of exposure to cause clinically recognisable changes, whereas strong irritants may cause observable changes within a few minutes. Contact dermatitis ranges from transient redness to severe swelling and bulbar formation. Itching and vesiculation are common. Medical attention is generally required.

The allergen induces constriction of the smooth muscle in the small bronchi and increased mucus secretion in the airways. This leads to airways obstruction and respiratory distress. The affected person should be removed from the source of the allergen, rested and kept warm. Medical advice should be obtained. Treatment with a bronchodilator may be required.

Conjunctivitis and rhinitis
Conjunctivitis requires medical attention and isolation from the allergen. Rhinitis is often only of temporary inconvenience and usually resolves after removal from exposure.

Cutaneous reaction
Anaphylaxis in the skin is characterised by the eruption of well circumscribed wheals with erythematous, raised edges and blanched centres. The lesions are pruritic and may occur anywhere on the body where contact is made with the allergen. The lesions reach maximum intensity in 15 to 20 minutes then slowly subside over the next 48 hours, but in some forms may become chronic.

Systemic reaction
An anaphylactic shock may occur in any individual who has a predisposition to an IgE mediated hypersensitivity reaction resulting from exposure to an allergen. Smooth muscle contraction is prominent with a fall in body temperature, hypotension, bradycardia and decreased serum complement levels. Circulatory shock with dizziness and faintness may be the only signs of the reaction but collapse, unconsciousness and death can occur. The most common causes of systemic reactions are injection of drugs such as penicillin, or the more natural occurrence of a bee sting. If systemic shock occurs the individual requires rest and warmth. Always get medical attention.

Arthus reaction
This response is indicated by an inflammatory necrotic lesion marked by oedema and haemorrhage at the site of injection of a soluble antigen to which the individual is sensitised. Lesions are not limited to skin but may occur in any vascular organ such as stomach, liver, kidney, brain and joints. The lesions generally reach maximum intensity in 2 to 5 hours and may take several days to resolve. Medical advice should be obtained if an Arthus reaction is suspected.

Antigens may attach to cell membranes and function as haptens. The red cell hapten complex may induce an immune response in which the antibody reacts with the allergen on the cell surface causing lysis through activation of complement. This haemolytic reaction is normally drug-induced but can also be caused by many laboratory chemicals. Affected persons should seek immediate medical attention.

Swelling of lymph nodes may occur in allergic response. The onset of swelling is usually rapid and can last for several days during which time the lesions can often be painful. The lymph nodes most commonly involved are those found in the neck but other areas of the body may also be affected.



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