With the arrival of summer comes a rather less welcome arrival – that of seasonal allergic rhinitis, more commonly known as hay fever. In the UK, an estimated 10-15% of the population are affected, a figure that is also on the rise. Despite the pollens of trees, grasses and weeds being the origin of hay fever, it’s a chemical produced in our bodies that’s actually to blame for the symptoms – and we’ve got the chemicals in medications for hay fever to thank for relief from these symptoms.
The course of events that leads to hay fever’s symptoms begins with exposure to pollens, which the body in affected individuals mistakenly identifies as a threat. To combat this threat, the body triggers the release of the Immunoglobulin E antibody (IgE). This antibody attaches to mast cells and basophils, which are types of cells found in the body, and particularly in exposed sites such as the skin.
Further pollen exposure causes the molecules in the pollen to bind to this antibodies on the outside of the mast cells, which then causes the mast cells to release a number of chemicals, including histamine. Histamine is the chemical responsible for the inflammatory response to allergens, the symptoms of which can include a runny nose, itching, sneezing and congestion.
Many of the medications used to combat hay fever work by affecting the response process involving histamine in some way. The most common class of compounds used are known as antihistamines; these compounds include molecules such as cetirizine and loratadine. They work by binding to the H1 receptors that histamine usually binds to, preventing it from inducing an inflammatory response to the allergens.
Antihistamines are available as tablets or nasal sprays. They are effective at limiting the majority of symptoms, though they have little effect on blocked noses. Another limitation is that they cannot reverse the effect of histamine that is already bound to the receptors. For this reason they are less effective if taken after an allergic response has already occurred, and more effective when taken in advance at the start of the day. First generation antihistamines can also lead to drowsiness; second generation versions, especially loratadine, are much less likely to cause this sedative effect. These medications only require administration once per day to achieve their effect.
If you’ve ever used eye drops to combat the itchy eyes often caused by hay fever, it’s possible that the active ingredient was sodium cromoglicate. This chemical also combats histamine – but in a slightly different way. Rather than interacting with the receptors that histamine binds to, sodium cromoglicate prevents symptoms by stabilising mast cells, and preventing them from releasing histamine in response to allergens in the first place. It’s not known exactly how it achieves this effect, but the end result is a relief of eye itchiness when used in the form of eye drops – and unlike antihistamines, it’s also effective is used after the onset of symptoms. It can also be used in the form of a nasal spray to control nasal symptoms, but requires more regular dosing than antihistamines.
Another class of medications that can be used to treat the symptoms of hay fever are corticosteroids. These are in fact the most effective of the drugs available, and they also work in a slightly different way to antihistamines. Rather than blocking the release or action of histamine, they merely mitigate the inflammatory symptoms, providing relief. However, they can take several days to build up to their full effect, so it can be useful for hay fever sufferers to start taking it a week or so before their symptoms usually occur. It can also be used in addition to antihistamines if your hay fever is truly horrendous.
There are other general actions you can take to reduce symptoms as well, but these tend to be variants on the rather unconstructive ‘just avoid ever leaving the house’. So, it’s something of a relief that we have these various classes of medication at our disposal to prevent us from becoming house-bound recluses!
References & Further Reading