Allergic Rhinitis

Allergic rhinitis affects approximately 1 in 4 people in Singapore — making it one of the most prevalent chronic conditions in the country. It is frequently dismissed as 'just allergies', yet for the many people whose symptoms are persistent and poorly controlled, it significantly disrupts sleep, work productivity, concentration, and quality of life.

Understanding what allergic rhinitis actually is, which allergens are most relevant in Singapore's climate, and what effective treatment looks like — including treatments that go beyond antihistamines — is the starting point for managing a condition that is very treatable when approached correctly.

What Is Allergic Rhinitis?

Allergic rhinitis is an immune-mediated inflammatory condition affecting the lining of the nose (nasal mucosa). It occurs when the immune system identifies a harmless airborne substance — an allergen — as a threat and mounts an exaggerated defence response, releasing immunoglobulin E (IgE) antibodies and triggering the release of histamine and other inflammatory mediators.

These mediators cause the characteristic symptoms: inflammation and swelling of the nasal lining, excess mucus production, and sensitisation of nerve endings that cause itching and sneezing. The same inflammatory response frequently extends to the eyes (allergic conjunctivitis), the sinuses (allergic sinusitis), and — via shared mucosal tissue — to the lower airways (asthma).

Allergic rhinitis is classified in two ways that are clinically useful for treatment planning:

By timing

• Intermittent AR — symptoms occurring fewer than 4 days per week or fewer than 4 consecutive weeks
• Persistent AR — symptoms occurring more than 4 days per week AND more than 4 consecutive weeks

By severity

• Mild — symptoms are present but do not impair sleep, daily activities, work, or school
• Moderate-severe — symptoms impair one or more of: sleep quality, daily activities, work or school performance, or leisure activities

Allergen Triggers in Singapore

In countries with distinct seasons, pollen is the primary trigger for seasonal hay fever. Singapore has no cold winter to interrupt plant growth and no distinct pollen season — which means most allergic rhinitis here is perennial (year-round) rather than seasonal, driven primarily by indoor allergens.

• House Dust Mites (HDM): By far the most common trigger in Singapore, accounting for the majority of confirmed allergic sensitisation. Dermatophagoides pteronyssinus and D. farinae thrive in Singapore's warm, humid climate. They live in mattresses, pillows, soft furnishings, and carpets — feeding on shed skin cells. Their faecal particles and body fragments are the allergenic material.
• Cockroach Allergens: Cockroach allergen — particularly Blatella germanica and Periplaneta americana — is a significant trigger in Singapore and other tropical urban environments. Cockroach proteins are found in household dust and can persist for months after the cockroach population is controlled.
• Mould and Fungal Spores: High ambient humidity promotes mould growth in bathrooms, air-conditioning systems, refrigerator seals, and poorly ventilated areas. Aspergillus, Cladosporium, and Alternaria are the most allergenic genera. Airborne spore counts are elevated year-round.
• Pet Dander: Proteins from cat skin (Fel d 1) and dog dander are potent allergens. They are extremely small, remain airborne for hours, and persist in homes long after a pet has been removed. Cat allergy is more common and more severe than dog allergy.
• Pollen: While not seasonal in Singapore, pollen from local trees and grasses contributes to perennial exposure. Some patients are sensitised to tropical tree pollens or grass pollens found year-round. International patients may also carry sensitisation from their home countries.
• Occupational Allergens: Certain occupations carry elevated allergen exposure — flour and grain dust (bakery workers), latex (healthcare workers), wood dust, chemicals, and animal proteins. Occupational allergic rhinitis may only occur in the workplace setting and requires specific enquiry.

Symptoms of Allergic Rhinitis

The nasal symptoms of allergic rhinitis are consistent and recognisable. Associated symptoms affecting the eyes, throat, and chest are common and clinically important.

Nasal Symptoms

• Nasal congestion: Blocked or stuffy nose, often worse in the morning or at night
• Sneezing: Often in prolonged bursts, particularly on waking or after exposure to a trigger
• Clear, watery rhinorrhoea: Runny nose with thin, watery discharge
• Nasal itching: An urge to rub or pick the nose; the 'allergic salute' (repeatedly wiping the nose upward) is characteristic in children
• Postnasal drip: Mucus trickling down the back of the throat causing sore throat, throat-clearing, or cough
• Reduced or absent sense of smell (hyposmia or anosmia): Particularly with nasal polyps

Eye Symptoms

• Itchy, red, and watery eyes: One of the most distinguishing features from the common cold
• Swelling of the eyelids
• Sensitivity to light

Systemic and secondary symptoms

• Fatigue and poor concentration: Often from disrupted sleep due to nasal obstruction
• Headache and facial pressure: From sinus congestion
• Mouth-breathing and snoring: Particularly in children whose nasal obstruction causes them to breathe through the mouth at nightt

Lower airway symptoms - the rhinitis-asthma link

The nose and lungs share the same mucosal lining and the same allergic inflammatory mechanism. In patients who have both allergic rhinitis and asthma — a combination sometimes described as 'one airway disease' — the conditions perpetuate each other. Poorly controlled rhinitis makes asthma harder to control, and untreated rhinitis in a patient without current asthma significantly increases the risk of developing it.

• Wheezing, chest tightness, and shortness of breath suggest asthma co-existing with rhinitis
• A dry, irritating cough, particularly nocturnal, may be the only asthma symptom in some patients

Complications of Untreated Allergic Rhinitis?

Allergic rhinitis that is inadequately managed can lead to several complications, each of which may require its own assessment and treatment:

• Recurrent sinusitis: Chronic nasal inflammation impairs sinus drainage, predisposing to bacterial sinus infections; patients with more than 3 episodes per year warrant investigation
• Nasal polyps: Overgrowth of the inflamed nasal lining that causes progressive obstruction, loss of smell, and poor response to standard medication; often requires specialist ENT management and may require surgery
• Asthma development or worsening 
• Eustachian tube dysfunction and otitis media: Chronic nasal inflammation extends to the Eustachian tube, causing ear congestion, muffled hearing, or recurrent ear infections, particularly in children
• Sleep-disordered breathing: Nasal obstruction disrupts sleep architecture and is a contributor to obstructive sleep apnoea in both adults and children
• Orthodontic and facial development problems in children: Chronic mouth-breathing from nasal obstruction is associated with altered dental and facial development in growing children; early treatment of rhinitis is important
• Impaired quality of life: Poor sleep, reduced concentration, impaired work performance, and social impact from persistent symptoms

Reducing Allergen Exposure in Singapore: Practical Measures

Imaging of the sinuses to assess chronic sinusitis, sinus anatomy, and extent of nasal polyps. Indicated when surgery is being considered or when sinus complications are suspected.

House Dust Mite Control

• Use allergen-impermeable covers on mattresses, pillows, and duvets — wash weekly at 60°C or use a tumble dryer at high heat
• Wash bedding weekly at 60°C minimum — lower temperatures do not kill mites
• Replace carpets with hard flooring in bedrooms — carpets harbour mite populations that cannot be eliminated by vacuuming alone
• Use a HEPA vacuum cleaner — standard vacuums release mite particles back into the air
• Maintain indoor humidity below 50% with air-conditioning — mites cannot survive at low humidity
• Remove soft toys from the bed; wash them regularly or freeze overnight to kill mites

General Measures

• Keep pets out of the bedroom and off upholstered furniture; bathe pets weekly
• Control cockroach access with pest management; seal food and rubbish
• Address mould — clean bathrooms and refrigerator seals regularly; service air-conditioning regularly
• Use air purifiers with HEPA filters in bedrooms, particularly for patients with persistent symptoms
• Shower and change clothing after outdoor exposure if grass pollen is a confirmed trigger

How is Allergic Rhinitis Diagnosed?

Diagnosis begins with a thorough clinical history — the pattern of symptoms, timing, environmental context, and associated conditions. Several tests are used to confirm allergic sensitisation and characterise the condition.

• Skin Prick Testing (SPT): Small amounts of allergen extracts are applied to the forearm and the skin is pricked. A positive response (wheal and flare within 15 minutes) indicates IgE-mediated sensitisation. Fast, inexpensive, and highly sensitive — the preferred first-line allergy test.
• Specific IgE Blood Test (RAST/ImmunoCAP): Measures IgE antibodies to specific allergens in the blood. Preferred when skin testing cannot be performed (severe eczema, antihistamine use, certain medications). Can test multiple allergens simultaneously including molecular components.
• Nasal Endoscopy: A thin flexible or rigid endoscope examines the nasal passages and nasopharynx. Identifies nasal polyps, septal deviation, adenoid enlargement, and anatomical factors contributing to nasal obstruction. Essential when surgical assessment is considered.
• Nasal Provocation Test: Direct application of an allergen to the nasal mucosa under controlled conditions to confirm clinical relevance of a sensitised allergen. Used for occupational rhinitis or when skin test and history do not align.
• Peak Nasal Inspiratory Flow (PNIF): Measures nasal airflow and objectively quantifies nasal obstruction. Useful for monitoring treatment response and documenting severity objectively.
• CT Sinuses: Imaging of the sinuses to assess chronic sinusitis, sinus anatomy, and extent of nasal polyps. Indicated when surgery is being considered or when sinus complications are suspected.