L16: Minor Ailments - Allergies and Hay fever

• Allergy

  The immune system reacting to a normally harmless substance
• Allergen


  A substance that triggers an allergy
• Factors that make people more prone to allergy

  • Hereditary
  • Gender
  • Race
  • Atopy
  • Age
• Environmental factors that can cause allergy


  • Environmental pollution
  • Allergen levels
  • Dietary changes
  • Early exposure may be protective
• Atopy


  The tendency to have an allergy
• Some allergy disorders

  • Asthma
  • Eczema
  • Hay fever
• Allergic reaction

  1. Allergen enters body

  2. Activates B cells to produce IgE

  3. Antibodies bind to mast cells

  4. Mast cells degranulate and release histamine

  Future exposure to allergen - primed mast cell degranulate and histamine release into local tissue causing allergy symptoms
• Sensitization

  When a limited exposure to a very small amount of allergen can trigger a severe reaction
• Allergy symptoms can occur seconds or minutes after exposure to the allergen but some symptoms can be prolonged if the allergen has been ingested but it is very rare for an allergy symptom to happen after 24 hours
• IgE mediated reactions


  Type I (immediate) hypersensitivity
• Atopy


  Genetic predisposition to make IgE antibodies in response to allergen exposure

  Allergic rhinitis, allergic asthma, atopic dermatitis are most common manifestation of atopy
• Allergens - Type 1 Hypersensitivity

  • Proteins in foreign serums, vaccines etc
  • Plant pollens
  • Drugs
  • Foods
  • Insect products
  • Mold spores
• Histamine

  An autocoid/local hormone that binds to H1 receptors, causing blood vessel dilation, increased capillary permeability, smooth muscle contraction, and skin itching
• Actions of histamine on H1 receptors

  • Blood vessel dilation
  • Increased capillary permeability (oedema)
  • Smooth muscle contraction
  • Skin itching
  • Anaphylactic shock (circulatory collapse and bronchoconstriction)
• Triple response of Lewis

  The skin reaction observed when the skin is scratched, caused by histamine

  1. Red line (15s) - Capillary dilation
  2. Flare around line (45s) - Arteriolar dilation
  3. Wheal (3min) - Exudation of fluid
• Symptoms of an allergy

  • Sneezing
  • Wheezing
  • Sinus pain
  • Runny nose (rhinorrhoea)
  • Cough
  • Vomiting
  • Diarrhoea
  • Urticaria (hives)
• Preventions for allergies

  • Allergen avoidance
  • Carry medical ID tag/bracelet
  • Carry emergency medicines (e.g. EpiPen)
• Allergic rhinitis


  Inflammation of the inside of the nose resulting in sneezing attacks and nasal discharge or blockage
• Long-term problems of allergic rhinitis

  • Nasal polyps - benign sacs of fluid in nasal passages and sinuses
  • Sinusitis - infection cause swelling and inflammation preventing mucus drainage from sinuses
  • Middle ear infections
• Types of allergic rhinitis

  • Seasonal (hay fever)
  • Perennial
  • Occupational
• Seasonal (hay fever) allergic rhinitis

  Usually caused by outdoor allergens, pollen and mould, with symptoms occurring less than 1hr a day and usually less than 4 weeks
• Perennial allergic rhinitis

  Caused by indoor allergens such as house dust mites, moulds, animal dander, with symptoms occurring year-round constantly for more than 4 weeks
• Occupational allergic rhinitis

  Caused from allergens at work such as dust from wood, flour or latex
• Non-pharmacological management of allergic rhinitis

  • Monitor pollen counts, keep windows closed/stay indoors, wear wrap-around sunglasses
  • Exclude pets from certain living areas, use acaricidal sprays and bedroom cleaning regimens, minimise carpets, soft furnishings and allergen-impermeable fabric bedding, use saline nasal washes
• Pharmacological management of allergic rhinitis

  • H1 receptor antagonists (antihistamines)
  • Mast cell stabilisers
  • Intranasal corticosteroids
  • Intranasal decongestants (local vasoconstrictors)
• Antihistamines

  H1 receptor antagonists that reverse the binding of histamine to the H1 receptor, more effective at preventing than reversing symptoms
• 1st generation antihistamines


  • Chlorphenamine (piriton), diphenhydramine, promethazine
• 1st generation antihistamines

  • Relatively non-selective for H1 receptors, lipophilic so cross blood-brain barrier, cause sedation, dizziness, fatigue, anti-muscarinic effects
• 2nd generation antihistamines

  • Cetirizine, loratadine, fexofenadine, acrivastine
• 2nd generation antihistamines


  • More selective for H1 receptors, less penetration of CNS, less sedating, lack anti-muscarinic effects but rare potential risk of cardiac arrhythmias
• Mast cell stabilizers

  Drugs like sodium cromoglicate that prevent histamine release, need to be used regularly while exposed for 4 times a day - for itchy and runny eyes

  Contains preservative so avoid with contact lenses
• Intranasal corticosteroids

  Beclomethasone, fluticasone and mometasone - most effective treatment for allergic rhinitis, reduce local inflammatory response and improve rhinorrhoea, itchiness, sneezing and congestion, have minimal systemic absorption

  Several days to obtain effect and several weeks for full effect
• Local vasoconstrictors (nasal decongestants)

  Drugs like phenylephrine, oxymetazoline and xylometazoline that constrict dilated arterioles in nasal mucosa to reduce airway resistance by mimicking noradrenaline and to bind alpha-adrenoreceptors - in form of nasal drops or spray with rapid action
• Rhinitis medicamentosa

  Rebound congestion following overuse of nasal decongestants, pathophysiology unknown but may be due to decreased local noradrenaline production
• Differential diagnosis of allergic rhinitis vs cold

  • Seasonal variation vs perennial
  • Duration (colds usually over in 2 weeks)
  • Rapid onset of symptoms with exposure
  • Rhinorrhoea characteristics (profuse and watery vs viscous)
  • Sneezing patterns
  • Cough and sore throat
  • Nasal itch and eye symptoms
  • Loss of smell
• When to refer for allergic rhinitis: when symptoms not controlled despite treatment, when nasal obstruction fails to clear (possible polyp), when orbital cellulitis (infected eyelids causing swelling) or recurrent nosebleeds (epistaxis) present or photophobia