It’s that time of year again. As the sun comes out and shines, plants and trees come into blossom. Beautiful… and causing pain for millions. Summer is somewhat oxymoronic for me: it’s great looking at the weather forecast to see it’ll be sunny tomorrow, opposed with the dread of seeing the pollen count will be anything other than “low”. Seasonal allergic rhinitis or hayfever can be a nightmare, ruining that rare opportunity to get some much-needed vitamin D. First thing in the morning with itchy eyes, tickly throat and runny nose – brilliant. Having said that, I don’t only get these symptoms in the summer, there have been a few Christmases when I’ve had itchy eyes; I’ll blame the turkey. It’s always worse in the summer though, I’m glad I managed to get medication on prescription, otherwise, it’d be an expensive inconvenience.
The whole thing is caused by our fantastic immune systems overreacting to something which is actually innocuous – it’s nothing that’s going to do harm. The body attacks it with everything it’s got, trying to get rid of it. Mucous membranes leaking left, right and center making eyes and nose stream, itching to get us to scratch it all away, sneezing to expel it – like having a cold in the middle of the summer. It’s definitely more prevalent in recent generations, maybe I wasn’t exposed to enough dirt and fields as a child. Although that’s not my parents’ fault, I didn’t like getting dirty – always a well-presented child. Nothing’s changed much… I know far more people my age and younger that have hayfever and other allergies than I do my elders. Maybe my compromised immune system makes me more susceptible? A new area of research I’m sure I’ll get round to one day.
So billions of tablets, sprays and whatever else they’ve come up with this year are being sold to combat this summer destroyer. The culprit – histamine. This little molecule is usually pretty useful, but no… it’s turned against us. Histamine is made by cells of the immune system, hidden in connective tissue. It opens up the tiny blood vessels (capillaries) to make them more permeable to their pals white blood cells (leukocytes) who would normally do the business of destroying invaders. It’s got loads of functions around the body but it helps make the body more sensitive to itch (hypernociception) and get things nice and inflamed to let more of those lovely white blood cells get to work. None of this is useful when pollen goes up your nose, ends up binding to white blood cells sending out antibodies which bind to a fun mast cell which releases histamine and begins that familiar set of symptoms. For some, that increased itchiness even means a lovely red rash – thanks, histamine!
Antihistamines for allergies are aimed at those receptors on mast cells that cause you to feel rubbish. Cetirizine, loratadine (Claritin) and chlorphenamine (piriton) all work at this receptor – H1. They all work differently to try and stop the receptor telling the cell to release it’s histamine stores. The trouble with drugs generally is the myriad functions each receptor has: each receptor could have multiple functions both wherever that cell is, but other kinds of cells may also have the same receptor somewhere else for something completely different! This is why drugs aim to be a specific as possible to a receptor and a location. You’ll have heard of side-effects – being as specific to a receptor as possible decrease these effects around the body. In the case of antihistamines an example is that histamine in the brain acts to regulate sleep and wakefulness, so stopping it here causes drowsiness. It’s the same pathway I was chatting about last week. The brain isn’t connected to the bloodstream like most other parts of the body, there’s a thin barrier – the blood-brain barrier cleverly named. It means only certain things can cross over that meet specific criteria. So you design the drug that it doesn’t meet those criteria. A simple concept, but drug discovery and design are definitely extremely difficult. Sometimes that’s why a drug is chosen to be specific to one particular area, by controlling how it is administered. If you’re taking a tablet, the hope it that it gets into the bloodstream which goes all around the body. That may mean only a small concentration of the drug gets to where you need it if your target is really common. For antihistamines nasal sprays and eye drops are a good example; they get to where they need to go, limiting the side effects and usually do their job quicker.
That’s the point of antihistamines, but they’re far from ideal and don’t work to stop symptoms 100%. Of course, there are many types of antihistamine because there are other types of histamine receptor elsewhere with other functions, so they’re not only given for allergies. But a similar inflammatory response is seen in the common cold, which I find helps, but there is only weak evidence to show this actually is effective – so perhaps it’s just a placebo effect with me. An extreme treatment for extreme symptoms would be immunotherapy. This involves giving the body small doses of the specific problem allergen, e.g. grass pollen, weed pollen, in small doses over a long period. It essentially trains the immune system to recognize it as harmless. This has been a treatment for a while and commonly involves trips to get injections on a regular basis. Recently there’s been a tablet that dissolves under the tongue (referred to as sublingual by the way) which is a quick way into the bloodstream; it still involves the long-term training of the immune system but makes it easier to use. It’s just grass pollen extract – the bit that the antibodies would be attacking the help the body get used to it. Clever stuff!
When drugs have failed and before the time of the pharmaceutical industry, nature has always provided a helping hand. Vitamin C is a known antihistamine and things like chillis, garlic, honey, and carrots can all help the symptoms like congestion, or protect your body in the first place. Capsaicin for example found in chili peppers helps to decrease congestion as well as garlic. Carotenoids found in carrots, pumpkins, sweet potatoes and others are antioxidants that can be anti-inflammatory. As in many drugs, nature provides a solution. Not that natural remedies are necessarily better, but if they work, obviously it’s worthwhile. I’m sure that’s a debate for another time.
I don’t think I’ll ever win the war against hayfever but it’s ruined so many summer days so far, I’m willing to fight it. I’ve found wearing my contact lenses actually helps if I can get them in quickly enough; sort of makes sense if they form a barrier, but then the pollen still gets breathed in so the other symptoms still occur. It’s been better though, so that’s one battle won. I’m taking Piriton (chlorphenamine) which works best before symptoms occur and I have few side effects, definitely no drowsiness. The side effects seem to decrease as the body gets used to the drug. Usually, it’s too late for the drug to be most effective – itchy eyes are my worst symptom and the first, as soon as they twitch, I’m running towards the tablets! The war continues then: timing it right, maybe researching when it’s going to be a bad day, research will always help to understand allergies and how to better combat them, especially for the worst affected. Trying to suppress the immune system can never be a good thing, it’ll leave you open to goodness knows what else, but I don’t think the drugs last long enough in the body to do anything. Maybe over a longer time, there would be an effect – taking any drug for years is going to result in some sort of unwanted effect. So that’s how the drugs work, and maybe you’ve learned something – so go away and dry your eyes, tomorrow might be a low pollen day…
Here’s a quick video for all you visual learners and the infographic below for a nice summary of the facts.
Disclaimer: please don’t be taking any drugs just because I said they work, I’ve been prescribed them. There are pharmacists and GPs for a reason – seek medical advice, especially if you have a pre-existing medical condition.