Your Blood Type Might Be Why Mosquitoes Love You. A Doctor Explains Why

Summer is by far our favorite season. The warm temps and sunny weather mean we can spend more time outside doing things we love, particularly around water (which is a perfect breeding ground for mosquitoes). 

What was once brushed off as a (mostly) harmless nuisance has become something you should pay closer attention to. As mosquito populations grow and climate patterns shift, doctors are seeing more people get seriously sick from diseases these tiny bugs carry.

"Both globally and in the US, we have seen increasing cases of mosquito-borne illnesses over the past decade," says Dr. Scott Braunstein, chief medical officer at Sollis Health.

While not every mosquito bite will lead to a severe disease, it's worth knowing the signs and how to protect yourself. According to Braunstein, here's what to look for.

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Did you know mosquitoes are the world's deadliest animal?

Mosquitoes may be tiny, but they're responsible for more deaths than any other creature on the planet. According to the World Health Organization, more than 700,000 people die each year from vector-borne illnesses that can be caused by parasites, viruses or bacteria. That includes everything from malaria and dengue to Zika virus, yellow fever, chikungunya fever and other viral infections that are difficult to treat once contracted.

Malaria alone caused nearly 600,000 deaths globally in 2023, mostly among children in Sub-Saharan Africa. Dengue affects roughly 390 million people annually, with around 20,000 deaths each year. And Zika virus, while rarely fatal, has been linked to severe congenital disabilities and neurological complications. Yellow fever, another mosquito-borne disease, can cause deadly liver failure in unvaccinated travelers.

These illnesses aren't limited to tropical regions anymore. The viruses mosquitoes carry are expanding to new areas and reemerging in places they haven't been seen in decades.

Why do mosquitoes bite?

Contrary to what you might think, mosquitoes don't bite people for food; they feed on plant nectar. Only female mosquitoes bite, and they do so to receive proteins from your blood needed to develop their eggs. 

What are the most common mosquito-borne illnesses in the US?

While the majority of mosquito bites result in welts that heal in a few days, mosquitoes are known carriers of many deadly diseases and illnesses, including but not limited to:

• Malaria
• West Nile
• Dengue
• Chikungunya
• Yellow fever
• Zika Virus

If you're in the US, the most likely mosquito-borne infections are West Nile virus and other types of encephalitis viruses (brain inflammation). Both can be mild, but in some cases, these infections can affect the brain and nervous system. Regarding travel-related cases, "Malaria, dengue and chikungunya are the most common," Braunstein says. "In the last few years in the US, we have seen sporadic increases of locally acquired cases of malaria and dengue."

While malaria and other mosquito-borne diseases hit Sub-Saharan Africa the hardest, mosquitoes pose a risk to every continent and nation. Most types of mosquitoes in the US are nuisance mosquitoes -- mosquitoes that do not spread germs that make people sick -- but there have been outbreaks of West Nile, dengue, chikungunya and Zika in a few states and territories. 

Several steps can be taken to control mosquito populations and minimize risk. Make sure to properly cover and store water containers around your home and drain any standing water to prevent mosquitoes from laying eggs. For treatments, you can use an outdoor adulticide to kill adult mosquitoes or larvicides to treat bodies of standing water that will not be used for drinking and cannot be drained. 

Infected bites will often look extremely red, swollen and warm or have a red streak that spreads outward from the bite. See a health care provider if you have signs of infection or if symptoms worsen. 

For more, read about the five smart ways to repel mosquitoes this summer, the mosquito forecast tool launched by Google and Off, and how you can make your own DIY traps for mosquitoes, hornets and other flying pests.

When to worry about your symptoms

According to Braunstein, about 25% of people who get one of these illnesses from a mosquito bite will develop symptoms. The earliest signs tend to be subtle and flu-like: "most commonly fever, joint pain and headache."

The more serious symptoms are harder to ignore and will require medical attention.

"If you begin to feel weak or dizzy, short of breath or develop neck stiffness or confusion, these could be signs of infection reaching your spinal fluid, and it's critical to seek immediate emergency care," Braunstein says.

Certain groups are more likely to develop severe illnesses, including children, older adults and people with compromised immune systems. Even your blood type can affect your likelihood of getting a mosquito bite. "People with Type O blood are the most attractive to mosquitoes, while those with Type A blood are the least attractive," Braunstein adds. "Mosquitos are attracted to warmer body temperatures, sweat and dark-colored clothing."

Not all mosquito bites are created equal, but they look the same

Identifying which mosquito bites are infectious from those that are not is where it starts to get tricky. You can't tell from looking at a bite whether it's harmless.

"Mosquito bites generally look and feel the same, whether the mosquito is carrying a serious disease or not," Braunstein says. But if the area around the bite starts to swell rapidly, feels painful or shows signs of infection like pus or redness, that's a reason to check in with your doctor. The same can be said for full-body symptoms like fever, joint pain or hives, especially if you have trouble breathing.

Why are some people more prone to bites?

There are several factors that impact why some people are more prone to mosquito bites than others:

Blood type

A common belief is that mosquitoes are attracted to certain blood types, considering mosquitoes bite humans for their blood. Blood type is determined by genetics, and each blood type is created based on the different sets of specific proteins, called antigens, on the surface of red blood cells. There are four main blood types: A, B, AB and O. 

While there are no firm conclusions as to which blood type is more attractive to mosquitoes, several studies have suggested people with type O are most appetizing to mosquitoes. A 2019 study observed mosquito feeding behavior when presented with different blood type samples, and found mosquitoes fed from the type O feeder more than any other. A 2004 study also found that mosquitoes land on blood group O secretors (83.3%) significantly more than group A secretors (46.5%).

However, these studies are not definitive, and much is still up in the air about mosquito preferences when it comes to blood type.

Clothing color 

Mosquitoes are highly visual hunters when it comes to finding a human to bite. This means movement and dark clothing colors like black, navy and red can stand out to a mosquito. Research has shown that mosquitoes are more attracted to the color black, but there has been little additional research into why this is the case. 

Carbon dioxide

Mosquitoes use sight and smell to find hosts to bite. One of the quickest ways mosquitoes can sniff out a person is through the carbon dioxide emitted when we breathe. According to research published in the journal Chemical Senses, mosquitoes use an organ called a maxillary palp for carbon dioxide detection and can sense it from 164 feet away. 

Because carbon dioxide is a huge attractor, people who emit more of it -- larger individuals and people who are breathing heavily when working out -- are more attractive to a mosquito. 

Body odor and sweat

Mosquitoes are attracted to more substances and compounds than just carbon dioxide. Mosquitoes can find people to bite by smelling substances present on human skin and in sweat, including lactic acid, uric acid and ammonia. 

A new study found that mosquitoes are attracted to compounds called carboxylic acids that every human produces through sebum, a waxy coating, on their skin. The sebum is eaten by the millions of beneficial microorganisms found on human skin, which produces more carboxylic acid -- and will, in turn, produce an odor similar to cheese or smelly feet that appears to attract mosquitoes. Lead researchers on this study said mosquitoes are sensitive to human odor and that even perfumes or colognes can't mask it.  

Researchers are still learning why certain body odors are more attractive to mosquitoes, but they do know that genetics, bacteria on the skin and exercise all play a factor. Genetics impact the amount of uric acid emitted, while exercise increases lactic acid buildup. 

Beer

In a small study, mosquitoes were observed to land on participants more frequently after consuming a small amount of beer. But before you swear off outdoor brews, know that the study only had 14 participants, and it found that mosquitoes may only be marginally more attracted to people who have been drinking beer.

Why do some people swell from mosquito bites more than others?

Mosquito bites can range in size from small spots to large welts. Why is this the case?

Bites affect people differently. The size and severity of a bite relate to how your immune system responds to the saliva introduced by the mosquito when it bites. When mosquitoes bite, they inject some saliva when drawing blood. This saliva contains certain anticoagulants and proteins, triggering the immune system to respond to these foreign substances. 

Our body responds by releasing histamine -- a chemical released by white blood cells when your immune system is fighting allergens -- which causes the itchiness and inflammation of the bite. 

Tips to avoid mosquito bites, according to a doctor

Here are some expert-approved tips to protect yourself from mosquito bites.

Avoid being outside during peak hours

The best way to protect yourself from mosquito-borne illnesses is to not get bitten in the first place. So your best bet is to avoid peak mosquito hours.

"To avoid being feasted on by mosquitoes is to avoid being outdoors at the time they are most active -- dawn and dusk," Braunstein says. If you do need to be outside, covering up matters: Wearing thick clothes, with long sleeves and pant legs, preferably lighter-colored clothing, can be protective.

Use a mosquito repellent

Regarding repellents, either DEET or a plant-based repellent be effective. "The main proven difference is that DEET provides longer-lasting protection (up to 5 hours), while plant-based repellants lose their efficacy quickly and require more frequent reapplication (every 1 to 2 hours)," says Braunstein. He notes that the American Academy of Pediatrics recommends no higher than 30% DEET for children. Insect repellents are also not recommended for children younger than 2 months.

Other mosquito repellent options you can consider:

• Spray clothing with permethrin (an insecticide)
• Try mosquito-repelling wristbands
• Use essential oils like citronella or eucalyptus
• Try a mosquito defense device

Clean up your yard

One of the simplest ways to reduce mosquitoes in your home is to eliminate stagnant water. This includes flower pots, bird baths and pet water bowls, which should be cleaned and emptied frequently.

Braunstein says, "These small pools are ideal breeding grounds for mosquitoes, especially in warm weather."

How to treat mosquito bites

Mosquito bites, while annoying, are often not severe and will resolve in a few days. In the meantime, there are several treatments to alleviate the itchiness and inflammation:

• Clean with rubbing alcohol if a fresh bite
• Take an oatmeal bath 
• Use over-the-counter antihistamines such as Benadryl or Claritin
  
• Apply mild corticosteroid creams
  
• Use aloe vera to reduce inflammation
• Try a cold compress or ice pack for 10 minutes

Though difficult, try as best you can to not itch the bite too roughly to prevent any sort of skin reaction or infection. 

How to stay on top of outbreaks

If you want to stay ahead of outbreaks in your area, Braunstein recommends checking out ArboNET, a resource from the CDC that tracks mosquito-borne diseases across the US. The database includes human cases, infected mosquitoes and veterinary cases. I find it particularly helpful during travel or seasonal spikes.

One last myth to ditch

You've probably heard someone say mosquitoes prefer "sweet blood" or that people with diabetes are more likely to get bitten. According to Braunstein, that's not how it works.

"People believe that mosquitoes prefer 'sweet blood,' for instance, after a high sugar meal or blood from those with diabetes," he says. "However, it has been shown that mosquitoes actually prefer the blood of people without diabetes, blood type O and are more attracted to carbon dioxide, lactic acid and ammonia in our sewers."

So no, it's not your dessert they're after. It's your scent, sweat and carbon dioxide that attracts mosquitoes.

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