Introduction

Mould, which is a type of fungus, can be a prevalent issue in countries that are humid and damp. In damp climates, it provides the desirable breeding grounds for fungi to release spores so that they can continually reproduce and spread. This can be problematic in many homes, which can lead to damaging health complications or allergies to the mould, and also impact an individual’s day-to-day life.¹ Prolonged mould exposure is a health risk, and great measures should be put in place to minimise contact.² Approximately 3-10% patients suffer from allergies associated with mould, and among the different variants of mould species, Alternaria alternata, Aspergillus fumigatus, Cladosporium herbarum and Penicillium notatum have a more pronounced increase in triggering allergic reactions.³ Therefore, this report focuses on mould allergies and the types of medicines that are used to treat the condition.

What are mould allergies?

Mould allergies can occur throughout the year. However, they are more common during the autumn months when the weather is mild and wet. Those who have mould allergies are due to the fungi spores, which cause the reaction. In an allergic reaction, the body detects something that is foreign and triggers the immune system to release a chemical in the body called histamine. This release of histamine causes symptoms such as a runny nose, sneezing and itching, and in rare cases, anaphylaxis, which is a life-threatening allergic reaction.^4,5

Symptoms

In patients with mould allergy specifically, symptoms include:

• Inflammation in the nose (causing sneezing and nasal congestion)
• Itchy eyes
• Skin rashes like eczema
• Asthma (or worsening of asthma)
• Lung conditions (Farmer’s lung and Sauna-taker’s lung)
• Coughing 
• Wheezing and shortness of breath^4,5

Treatment options

Removing oneself from the causative allergen (which in this case is mould) is the best option in preventing mould allergy symptoms. However, if this is not possible, then medications such as antihistamines, decongestants, corticosteroid nasal sprays, inhalers and immunotherapy can be used to treat symptoms.⁶

Antihistamines

There are three different types of antihistamines, and they are categorised by either being ‘first generation’, ‘second generation’ or ‘third generation’. ‘First-generation’ antihistamines such as chlorphenamine (Piriton®) and promethazine (Phenergan®) are the oldest and earliest forms of antihistamines produced and are more sedating. ‘Second generation’ antihistamines such as cetirizine (Piriteze®), loratadine (Claritin®) and fexofenadine (Allegra®) are newer forms and are less sedating, and ‘third generation’ antihistamines such as desloratadine (Neoclarityn®) are the newest forms of antihistamines. They are available in tablet form or as an oral solution, in which Piriton®, Phenergan®, Piriteze®, Claritin® and Allegra® tablets can be bought over the counter in UK pharmacies.⁷

Mechanism of action

Antihistamines used for allergies target the specific H₁ histamine receptors and compete with histamine. H₁ histamine receptors are proteins that get switched “on” when histamine binds to them, specifically on the 3^rd and 5^th domains. Antihistamines are not structurally similar to histamines and bind to a different part of the receptor. For example, cetirizine binds to the 4^th and 6^th domains to switch the receptor “off” and prevents histamine from producing its undesirable effects.⁸

‘First-generation’ antihistamines have a duration of action between four to six hours and can cross the blood-brain barrier into the central nervous system to target H1 histamine receptors, and this gives it a more sedating profile in comparison to ‘second-generation’ and ‘third-generation’ antihistamines, which are less sedating. ‘Second-generation’ antihistamines can have an effect between 12 to 24 hours.⁹

Side effects

Although antihistamines are generally safe to take for many patients, they can come with adverse effects:

• Sedation/drowsiness (especially in ‘first generation’ antihistamines)
• Dry mouth
• Insomnia
• Dizziness
• Tinnitus (constant ‘ringing’ in the ears)
• Headache
• Fatigue
• Rash
• Impaired concentration and memory (‘first generation’ antihistamines)^7,9

Decongestants

Decongestants can be classed as nonselective, such as phenylephrine (Sudafed PE®) and pseudoephedrine (Sudafed®), which are available in tablet or solution forms. They can also be selective, such as xylometazoline (Otrivine®) and oxymetazoline (Sinex®) in the form of nasal sprays. They are available over the counter in pharmacies to help with nasal congestion.¹⁰

Mechanism of action

After an allergic reaction, individuals may get a blocked nose. In nasal congestion, the nasal lining can become inflamed, and the small blood vessels in the nose can dilate and swell, causing it to be hard to breathe. The nose might also become runny to try to flush out the allergen. Decongestants work by binding to alpha adrenergic receptors (proteins found on vascular smooth muscle) or by promoting the release of noradrenaline (norepinephrine). By binding to the receptor, it causes smooth muscle to constrict. This decreases blood flow to the nasal passages as the blood vessels in the nose constrict, which allows you to breathe.¹⁰ 

Side effects

Because nonselective decongestants bind to α and β receptors, and β receptors are commonly found on the heart, individuals may experience symptoms involving the heart while taking decongestants (like Sudafed®), such as an increase in blood pressure. Decongestants, which are selective, primarily bind to α receptors and therefore do not impact the heart. Other adverse effects caused by decongestants include:

• Dry nasal passages
• Potential burning and tingling sensations in the nose (especially with nasal spray usage)
• Headache
• Dizziness
• Quickened heart rate (especially in nonselective decongestants)
• Rebound nasal congestion (in long-term nasal spray use)
• Dry mouth
• Nausea
• Feeling agitated or restless
• Rash
• Potential drowsiness in some decongestants^10,11

Corticosteroid nasal sprays

There are numerous corticosteroid (steroid) nasal sprays that can be bought over the counter in pharmacies. These are helpful to relieve nasal congestion initially or when decongestants have failed. They can also be taken alongside antihistamines to help with the additional allergy symptoms. Examples of corticosteroid nasal sprays include: fluticasone propionate (Pirinase®), fluticasone furoate (Avamys®) (which is a prescription-only medication), beclometasone dipropionate (Beconase®), mometasone furoate (Clarinaze®) and budesonide (Benacort®). Corticosteroid nasal sprays may also have an added antihistamine component, such as Dymista®, which contains fluticasone propionate and azelastine hydrochloride. Dymista® has recently been available as a medication that can be bought over the counter in pharmacies.¹²

Mechanism of action

Corticosteroids work by preventing the production and release of inflammatory mediators during an allergic reaction. This results in a reduction in inflammation in the nasal passages and improves breathing. It does this by binding onto the glucocorticoid receptor (which is a type of protein) to produce anti-inflammatory proteins and block the production of pro-inflammatory and immune proteins.¹³

Side effects

Inhaled corticosteroids are generally safe for individuals; however, some may experience adverse effects such as:

• Dry throat and nasal passages
• Sneezing
• Nose bleeding
• Headache
• Throat irritation
• Unpleasant taste (the drug being lost in the throat)
• Distorted sense of smell
• Partial or full loss of smell
• Potential shortness of breath
• Palpitations ¹⁴

Immunotherapy

In certain patients where all treatment options have been exhausted, immunotherapy could be an option to try. Immunotherapy, also known as allergen-specific immunotherapy, is not a common treatment due to the complexity of getting standardised allergenic moulds. The treatment involves patients steadily being exposed to increased doses of the mould in order to make the immune system less sensitive so that allergy symptoms become less severe and easier to manage. It is recommended for patients who have allergic rhinitis (hay fever) symptoms and those with mild asthma.¹⁵

Mechanism of action

In allergen-specific immunotherapy, when the body gets exposed to allergens in small dose increments, the body produces IgE antibodies, which bind to basophils and mast cells to release histamine and cause an allergic reaction. During this process, memory T cells (which provide innate immunity and recognise and attack the allergen after being pre-exposed to it) and memory B cells (recognise the allergen after being pre-exposed to it and create antibodies) get produced. These two cells play a role in providing long-term defence against reinfections from the allergen and cause the immune system to become desensitised.¹⁶ 

Side effects

As allergen-specific immunotherapy involves injecting the mould in the form of a vaccine, the most common adverse effects involve local skin reactions such as a rash. Other adverse effects include:

• Shortness of breath
• Cough
• Inflamed nasal passages, causing nasal congestion
• Allergic reactions (sneezing, watery eyes)
• Mild asthma symptoms
• Itching and mouth swelling
• Headaches
• Drowsiness^15,17

Summary

Mould allergies occur when individuals have an allergic reaction to the fungi spores, which causes symptoms like nasal congestion, sneezing, watery eyes and coughing. Long-term mould exposure is a health risk and can lead to detrimental health complications. The best treatment option to prevent the symptoms of mould allergy would be to avoid mould exposure. Medications can be used to treat symptoms such as antihistamines, decongestants, corticosteroid nasal sprays and immunotherapy. It is recommended to speak to a healthcare provider if you have persistent mould allergy symptoms despite trying different treatments.