What is Hay Fever?
Hay fever is a common allergic reaction which occurs at particular times of the year. It is known as seasonal allergic rhinitis, sharing symptoms with perennial (year-round) allergic rhinitis, but occurring as a reaction to pollen from grass, trees and weeds during the early spring and summer months. While hay fever frequently begins at a young age, it can affect both adults and children. Sometimes seasonal allergy symptoms fade over the years, only to reoccur later in life. For some, moving to a new location with different types of flora can alleviate symptoms or even eliminate them.
The same pollen and allergens that trigger seasonal allergy symptoms can cause asthma attacks, resulting in wheezing, shortness of breath, chest tightness and difficulty breathing. This condition is referred to as allergy-induced asthma or allergic asthma.
What Causes Hay Fever?
It is caused when the body makes antibodies (IgE) to certain substances, such as pollen, which are known as allergens.
Grass pollen is the most common allergen (May to July), but tree (February to June) and weed (June to September) pollens can also cause the allergic reaction we know as hay fever.
What are the symptoms?
- Itchy eyes/throat
- Sneezing, blocked/runny nose
- Watering, red eyes (allergic conjunctivitis)
- Headaches, blocked sinuses
- Shortness of breath
- The sensation of mucus running down the back of the throat, which can also be a symptom, and is called ‘post-nasal drip’.
Symptoms will vary depending on the pollen count.
Avoidance of the allergic triggers and the use of antihistamines. Often symptoms are managed by:
- Monitoring pollen forecasts daily and staying indoors with the windows closed when the count is high (generally on warmer, dry days). Rain washes pollen from the air so counts are normally lower on cooler, wet days
- Avoiding drying washing on a clothes-line outside when pollen counts are high
- Taking antihistamines, which are probably the best-known type of allergy medication, and most are readily available from a pharmacy without prescription
However, antihistamine medication isn’t for everyone. Remember, they don’t cure the allergies — they just treat the symptoms. In fact, many antihistamines are not recommended for people with high blood pressure, heart disease, kidney or liver disease, glaucoma, thyroid problems, or women who are pregnant or breastfeeding.
Theories as to why hay fever is on the rise
Allergies are considered as disorders of the immune system. The body over-reacts to harmless substances and produces antibodies to attack the substance. A person can be particularly susceptible to a weakened immune system after a physical trauma or surgery, underlying illnesses, or during times of emotional and physical stress.
Prolonged sleep restriction and the accompanying stress response invoke a persistent unspecific production of pro-inflammatory cytokines (chronic low-grade inflammation) and also produce immunodeficiency, which both have detrimental effects on health.
The Hygiene Hypothesis
The modern hygiene hypothesis suggests that increased risk of allergies is due to our insistence on cleanliness and lack of exposure to a wide range of microbes in the developed world, which deprives our bodies of immune stimulation, disrupting normal immune development.
The original hypothesis dates back to 1989 when David Strachan proposed that lower incidence of infection in early childhood could be an explanation for the rapid 20th century rise in allergic diseases such as asthma and hay fever. He reported that over the past century declining family size, improvements in household amenities, and higher standards of personal cleanliness have reduced the opportunity for cross infection in young families. This may have resulted in more widespread clinical expression of atopic disease, emerging earlier in wealthier people, as seems to have occurred for hay fever.
Changes in microbiome
Another factor is the relationship between gut health and allergy symptoms. This is something many would not consider; however, it is recognised that the gastrointestinal system plays a central role in immune system homeostasis. The crucial position of the gastrointestinal system is testified by the huge number of immune cells that reside within it.
Indeed, gut-associated lymphoid tissue (GALT) is the prominent part of mucosal-associated lymphoid tissue (MALT) and represents almost 70% of the entire immune system; moreover, about 80% of plasma cells (mainly immunoglobulin A (IgA)-bearing cells) reside in GALT. In addition, early-life environmental influences that are known to disrupt the microbiota, such as antibiotic use, caesarean birth, and formula feeding, are all associated with increased susceptibility to asthma and allergies later in life.
The histamine connection
Histamine is considered an important compound in the body. It acts as a neurotransmitter and regulates production of stomach acid, blood vessel permeability, and contraction of skeletal muscle. It is also a major component of the immune response and thus a key mediator in allergic reactions. A certain amount of histamine is required for proper physiological function; however, some people have a condition called histamine intolerance in which they produce excess histamine and/or have a deficiency in diamine oxidase (DAO), the enzyme that breaks it down. When this occurs, histamine can then be absorbed and be transported to various sites of the body, exacerbating allergic symptoms.
There are many possible causes of histamine intolerance including high consumption of histamine-rich foods, genetic factors when certain sequence variants (polymorphisms) in the DAO gene lead to a significantly reduced DAO enzyme activity, intestinal permeability and SIBO (small intestine bacteria overgrowth). So fundamentally a disturbance in the gut biome plays a significant role in creating histamine intolerance.
Taking probiotics that contain histamine-degrading strains such asBifidobacterium infantis, Bifidobacterium longum and Lactobacillus rhamnosus is recommended for those with histamine intolerance.
It is not surprising, therefore, that there appears to be a link between the severity of allergies and the health of the gut and its corresponding immune system and therefore, restoring a healthy balance of gut flora is the best long-term solution to resolving a histamine issue.
Histamine N-methyltransferase (HNMT) is an enzyme expressed in the central nervous system that specifically metabolises histamine. HNMT plays an important role in regulating histamine as it breaks down histamine at an intracellular level. It inactivates histamine by transferring a methyl group from S-adenosyl-L-methionine to histamine.
HNMT is expressed in many human tissues, with the highest levels found in the liver and kidneys, but also in the bronchi and trachea. HNMT is a key enzyme concentrated in the liver which is responsible for degrading histamines generated as a result of the functions of the body and in particular mast-cells. It plays an important role in degrading histamine and in regulating the airway response to histamine. Thus there is a link between histamine breakdown and methylation; poor methylation may contribute to allergies.
Recent studies have revealed that vitamin D has important functions in the immune system and might influence the course of immune-mediated disorders. Lower vitamin D levels have been associated with more allergic disease and elevated serum IgE.
In addition, magnesium is another nutrient to be considered. Vitamin D cannot be metabolised without sufficient magnesium levels. Magnesium consumption from natural foods has decreased in the past few decades, owing to industrialised agriculture and changes in dietary habits. Magnesium status is low in populations who consume processed foods that are high in refined grains, fat and sugar. In addition, high consumption of coffee, fizzy drinks, salt, alcohol, stress and vigorous exercise can also lower magnesium levels.