60 second summary
- Hayfever affects between 10-30% of the population
Burning, swollen eyes, bothersome fatigue, nose clogged and tender…
Affecting 10-30% of the general population hayfever, medically known as allergic rhinitis, is one of the most common allergies worldwide.
Allergic rhinitis- inflammation of the inside of the nose caused by an allergen, such as pollen, dust, mould or flakes of skin from certain animals.
What causes us to feel ill in hayfever?
Immune responses which trigger us to feel ill are usually triggered by antigens. These are molecules unique to the item they are on, found on bacteria, viruses, chemicals as well as our own cells. In a healthy individual, antigens on their own cells are recognised as ‘self-antigens’ and so are not attacked. Certain immune system cells, such as dendritic cells, process antigens from disease causing substances; Then the dendritic cells present the antigens on proteins they have on their surface called Major histocompatibility complexes.
When the antigen binds to these complexes this alarms the body of an intruder and leads to the start of the allergic reaction response.
How does our body react to the presence of a foreign molecule?
Firstly allergen specific cells called T helper cells must mature. T helper cells communicate to other cells that a dangerous substance is in the body– this allows recruitment of more immunity based cells to help. One method of communication between cells is by the release of molecules called cytokines. So T helper cells release these cytokines which are delivered on the other end of the line to B cells, which play a large role in destruction of the pathogen by producing antibodies. Antibodies are Y shaped proteins, serving a protective function by binding to antigens and neutralizing them.
However the release of these antibodies, IgE being a common example, comes at a cost as they can bind to other immunity related cells and release compounds such as histamine- the main mediator of itching. 
This is followed by common hayfever symptoms of include nasal itching sneezing, nasal obstruction and a runny nose.
Treatment with probiotics
Overall studies have already confirmed the therapeutic effect of probiotics in terms of inflammation. In one systematic review of several experiments looking at the use of probiotics in hayfever treatment, most showed evidence of a clinical benefit compared to a placebo. In another study the number of yearly hayfever episodes was significantly reduced with probiotic supplementation. What is still uncertain is what specific bacteria are the most effective but so far 2 strains have displayed their anti inflammatory value against hayfever in experiments:
- Lactobacillus paracasei– found in fermented vegetables
2. Bifidobacterium longum– found in certain strains of yoghurt. 
It is important to note however that the effect of the probiotics is lagged because it takes time for the gut to be colonized. Yet if you supplement your diet with these beneficial bacteria all year round when the hayfever season comes around you should notice milder symptoms. 
How do these microbes affect hayfever?
Despite the mechanisms of bacterial action in allergies still remaining in question, one hypothesis is that microbes decrease the symptoms of hayfever by increasing the proportion of regulatory T cells. These immune response suppressing cells can control antibody producing B cells ,mention above, decreasing overall inflammation.
Competing with other cells for resources such as growth factors, increased proportions of these regulatory cells stimulated by the right gut bacteria may be an effective method in control and containment of hayfever.
 PMC. (2010). The Pathophysiology, Diagnosis and Treatment of Allergic Rhinitis. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2846743/ [Accessed 12 Jul. 2019].
 PMC. (2016). A Systematic Review and Meta-analysis of Probiotics for the Treatment of Allergic Rhinitis. [online] Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4725706/ [Accessed 12 Jul. 2019].
 PMC. (2010). Probiotics in Treatment of Allergic Rhinitis. [online] Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651057/ [Accessed 12 Jul. 2019].