Female mos­qui­toes need blood to devel­op their eggs. Even though they take a tiny amount of our blood, they can leave us with itchy red lumps that can last days. And some­times some­thing worse.

So why does our body react and itch after being bit­ten by a mos­qui­to? And why are some peo­ple more affect­ed than others?

What happens when a mosquito bites?

Mos­qui­toes are attract­ed to warm blood­ed ani­mals, includ­ing us. They’re attract­ed to the car­bon diox­ide we exhale, our body tem­per­a­tures and, most impor­tant­ly, the smell of our skin.

The chem­i­cal cock­tail of odours from bac­te­ria and sweat on our skin sends out a sig­nal to hun­gry mosquitoes.

Some people’s skin smells more appeal­ing to mos­qui­toes, and they’re more like­ly to be bit­ten than others.

Once the mos­qui­to has made its way to your skin, things get a lit­tle gross.

The mos­qui­to pierces your skin with their “pro­boscis”, their feed­ing mouth part. But the pro­boscis isn’t a sin­gle, straight, nee­dle-like tube. There are mul­ti­ple tubes, some designed for suck­ing and some for spitting.

Once their mouth parts have been insert­ed into your skin, the mos­qui­to will inject some sali­va. This con­tains a mix of chem­i­cals that gets the blood flow­ing better.

There has even been a sug­ges­tion that future med­i­cines could be inspired by the anti-blood clot­ting prop­er­ties of mos­qui­to saliva.

It’s not the stab­bing of our skin by the mosquito’s mouth parts that hurts, it’s the mozzie spit our bod­ies don’t like.

Are some people allergic to mosquito spit?

Once a mos­qui­to has inject­ed their sali­va into our skin, a vari­ety of reac­tions can fol­low. For the lucky few, noth­ing much hap­pens at all.

For most peo­ple, and irre­spec­tive of the type of mos­qui­to bit­ing, there is some kind of reac­tion. Typ­i­cal­ly there is red­ness and swelling of the skin that appears with­in a few hours, but often more quick­ly, after just a few minutes.

Occa­sion­al­ly, the reac­tion can cause pain or dis­com­fort. Then comes the itch­i­ness.

Some peo­ple do suf­fer severe reac­tions to mos­qui­to bites. It’s a con­di­tion often referred to as “skeeter syn­drome” and is an aller­gic reac­tion caused by the pro­tein in the mosquito’s sali­va. This can cause large areas of swelling, blis­ter­ing and fever.

The chem­istry of mos­qui­to spit hasn’t real­ly been well stud­ied. But it has been shown that, for those who do suf­fer aller­gic reac­tions to their bites, the reac­tions may dif­fer depend­ing on the type of mos­qui­to biting.

We all prob­a­bly get more tol­er­ant of mos­qui­to bites as we get old­er. Young chil­dren are cer­tain­ly more like­ly to suf­fer more fol­low­ing mos­qui­to bites. But as we get old­er, the reac­tions are less severe and may pass quick­ly with­out too much notice.

How best to treat the bites?

Research into treat­ing bites has yet to pro­vide a sin­gle easy solution.

There are many myths and home reme­dies about what works. But there is lit­tle sci­en­tif­ic evi­dence sup­port­ing their use.

The best way to treat mos­qui­to bites is by apply­ing a cold pack to reduce swelling and to keep the skin clean to avoid any sec­ondary infec­tions. Anti­sep­tic creams and lotions may also help.

There is some evi­dence that heat may alle­vi­ate some of the discomfort.

It’s par­tic­u­lar­ly tough to keep young chil­dren from scratch­ing at the bite and break­ing the skin. This can form a nasty scab that may end up being worse than the bite itself.

Apply­ing an anti-itch cream may help. If the reac­tions are severe, anti­his­t­a­mine med­ica­tions may be required.

To save the scratching, stop the bites

Of course, it’s bet­ter not to be bit­ten by mos­qui­toes in the first place. Top­i­cal insect repel­lents are a safe, effec­tive and afford­able way to reduce mos­qui­to bites.

Cov­er­ing up with loose fit­ted long sleeved shirts, long pants and cov­ered shoes also pro­vides a phys­i­cal barrier.

Mos­qui­to coils and oth­er devices can also assist, but should not be entire­ly relied on to stop bites.

There’s anoth­er impor­tant rea­son to avoid mos­qui­to bites: mil­lions of peo­ple around the world suf­fer from mos­qui­to-borne dis­eases. More than half a mil­lion peo­ple die from malar­ia each year.

In Aus­tralia, Ross Riv­er virus infects more than 5,000 peo­ple every year. And in recent years, there have been cas­es of seri­ous ill­ness­es caused by Japan­ese encephali­tis and Mur­ray Val­ley encephali­tis viruses.

By Cameron Webb, Med­ical Ento­mol­o­gist, NSW Health Pathol­o­gy and Clin­i­cal Asso­ciate Pro­fes­sor and Prin­ci­pal Hos­pi­tal Sci­en­tist, Uni­ver­si­ty of Sydney

This arti­cle is repub­lished from The Con­ver­sa­tion under a Cre­ative Com­mons license. Read the orig­i­nal arti­cle.