define hypersensitivity
immune response that causes collateral damage to self due to an exaggeration of normal immune mechanisms
what is type 1 hypersensitivity mediated by?
IgE
what is type 2 hypersensitivity mediated by?
IgG
what is type 3 hypersensitivity mediated by?
immune complex
what is type 4 hypersensitivity mediated by?
T cell mediated
when do allergic reactions occur?
when a person’s immune system reacts to normally harmless substances in the environment
what is the hygiene hypothesis?
we live in a society so clean that our body is not used to many substances which we used to be exposed to regularly
when will a type 1 allergy occur?
immediately (within minutes - 2 hours after exposure)
what are the routes of exposure for type 1 allergies?
skin contact
inhalation
ingestion
injection
what aspects of the history would make you suspect a type 1 allergy?
consistent reaction with every exposure
what will a type 1 allergy lookalike clinically?
- urticaria (v itchy)
- angioedema
- wheezing/asthma
- anaphylaxis
what investigations would you do for a type 1 allergy?
- specific IgE test
- skin prick testing
- challenge testing
- serum mast cell tryptase level (during anaphylaxis)
how would you manage a type 1 allergy?
- allergen avoidance
- anti-histamines
- anti-inflammatory (corticosteroids)
- adrenaline autoinjector
- mast cell stabilisers (sodium cromoglycate)
- immunotherapy
- media alert bracelet
- information & education
when does a type 4 allergy present?
typically after 24-48 hours
delayed hypersensitivity
give an example of a type 4 allergy seen in dermatology
allergic contact dermatitis
name some common allergens that cause a type 4 allergy
- nickel
- thiuram in nitrile gloves
- colophony in elastoplast
- fragrance in deodorants
- chromate in leather
- garlic
- PDP in henna tattoos
- diethylthiourea (wrist splints)
- dermabond in surgical glue
- english Ivy
- gold
when are patch tests read?
at 48 hours & 96 hours
why are readings taken at both 48 & 96 hours?
type 1 allergies are delayed so should only be seen at 96 hours
what is irritant contact dermatitis?
non-immunological process, contact with agents that abrade, irritate & traumatise skin directly
give 2 examples of irritant contact dermatitis?
- nappy rash
- lip lick dermatitis
how are allergies managed?
- allergen/irritant avoidance or minimisation
- emollients
- topical steroids
- UV phototherapy
- immunosuppressants
