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Mosquito bites: Why they itch so much and how to stop scratching them (according to science).

By Belinda Smith for the ABC.

I rarely see my assailants as they disappear into the dusk, leaving no trace aside from the beginnings of a bump.

My attackers are, of course, those swarming suckers of summertime: mosquitoes. And there are plenty around at the moment, thanks to all this rain we've had.

Despite making every effort to avoid being bitten in the first place, especially as some mosquitoes carry potentially nasty diseases, the wily little things occasionally slip past my defenses.

And I have the unfortunate combination of being a mozzie magnet and reacting pretty severely to their bites.

Within minutes, welts spring up, each around the size of a 5 cent coin, surrounded by a spreading ring of reddening skin.

Then the itch sets in.

Almost as quickly as they swell, my bite sites start feeling a bit prickly, then tickly, before blooming into a full blown itch - the kind that seems to intensify right as I'm trying to sleep.

Over the years, I've received mountains of advice on how to relieve itchy mozzie bites: tips and tricks that people absolutely swear by.

But what does science say? What works? And what doesn't?

It starts with saliva

First, we need to know why mosquito bites look and feel the way they do.

Not everyone reacts the same way, and how we react changes with age and other factors (more on that later).

But essentially, it starts with mosquito saliva - specifically, a handful of compounds in it, says Catriona Nguyen-Robertson, an immunologist at the Peter Doherty Institute for Infection and Immunity.

"Mosquito saliva is very complex, with 100 or more different proteins in it.

"Of those, more than dozen, maybe around 16, have been identified to cause an immune reaction," she says.

A typical mosquito bite reaction has two parts. The first is the wheal - that's the raised lump.

"The wheal results from vasodilation, which means your blood vessels open up," Dr Nguyen-Robertson says.

"Your blood vessels also get a little bit more leaky, meaning that immune cells can now come out of the blood into the area.

"So that's why you get swelling - there's more liquid and cells getting to the area."

Then there's the flare: the ruddy patch circling the wheal.

Its redness and inflammation is a sign of an immune system chain reaction involving a kind of antibody called IgE, which triggers the release of chemicals such as histamines.

Histamines attract more immune cells to the area. They also prompt nerves in our skin to send a signal to our brain which makes the bite feel itchy.

Luckily for people like me, the inflammation and itchiness does wane over time.

"That wheal and flare response peaks at about 20 minutes post bite, but it can remain an issue for 24 to 36 hours, then typically resolves over seven to 10 days," Dr Nguyen-Robertson says.

Scratching a mozzie bite brings the risk of an infection. So how can you ditch the itch?

Scratching feels good, but it's a bad idea

The reason our body makes mozzie bites itch is so we literally dig the saliva proteins out of our skin, thus dispatching the invader.

But we shouldn't do it, regardless of how satisfying a good scratch might feel, says Cameron Webb, a medical entomologist at the University of Sydney and NSW Health Pathology.

"We want to avoid secondary infection in the bite.

"That's when they really turn nasty and scab over."

Children may have a harder time resisting the urge to scratch. When we're kids, our body makes more IgE antibodies, so we generally get a more powerful histamine response.

As time wears on, those antibody levels drop. And as we keep getting bitten, we tend to develop a tolerance to mosquitoes - but only the ones we're exposed to.

If you've ever gone away on holiday and had a massive reaction to the local mosquitoes there, it's because your body has encountered a new cocktail of saliva proteins, and sees them as a new threat to contend with.

Different mosquito populations might dine on different animals, so a group that feeds mostly on frogs could have quite different saliva to those that live on livestock blood.

Another possible reason to keep your fingernails away: lab studies have uncovered a potential link between a mozzie bite's itchiness and mosquito-borne disease transmission.

A UK study in mice found Semliki Forest virus and Bunyamwera virus - found in Africa and transmitted by mosquitoes - infected immune cells that flooded the bite site, which helped the viruses replicate and spread.

When the researchers suppressed inflammation at the site, viral infection dropped too.

What popular remedies work to alleviate an itch?

One popular method of relief is to run hot water over a metal spoon, then press the hot metal on the bite.

The idea is the heat from the spoon warps or denatures the histamines in our skin.

"If you denature histamines, then sure - they're not going to be able to do their thing," Dr Nguyen-Robertson says.

"But by heating up your skin proteins, how can you say the spoon is specifically denaturing histamines and nothing else?"

Any relief is probably due to the brain sensing heat, and that signal - which is a more pressing danger - overrides the itchy feeling, she adds.

A similar effect probably comes with making a cross on the bite with your thumbnail, or any other method which involves inflicting momentary pain on the site.

When the pain wears off, nothing's stopping the itchiness from returning.

What about slathering ointments or calamine lotion on your bites? They were summer staples in my house growing up.

Some liquids, like calamine lotion, can cool the skin as they evaporate, stimulating temperature nerves and hiding the itch.

Anti-itch creams available might contain a topical anesthetic such as lidocaine, or a corticosteroid to help reduce inflammation.

But just how well topical treatments work to relieve an itchy bite is hard to say, Dr Webb says.

"There's little conclusive evidence that they work in all circumstances.

"I think that's where one of our problems lies - I think maybe there is a bit of a placebo effect."

For me, they do very little, and the itch always comes back with a vengeance.

This is how I ditched the itch

In general, there's no single completely effective way to quell an itchy mosquito bite.

Dr Webb suggests washing the bite to get rid of any bacteria that might cause an infection, should the skin break, then put a cool pack on it.

That will contract the blood vessels in the area, and reduce swelling and inflammation.

Some studies suggest an over-the-counter antihistamine can help take the itch out of a bite too.

Antihistamines work by competing with and blocking the effects of the histamines our body produces - but they won't work all the time, or for everyone.

Only recently, after trying all manner of different anti-itch methods, did I find a remedy that works for me: an ice pack/antihistamine combo.

Good luck finding yours! And try to stop scratching.

- ABC Click here to read the full article (source).


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