Overview

Mosquito bites are the itchy bumps that appear after mosquitoes use their mouthparts to puncture your skin and feed on your blood. The bump usually clears up on its own in a few days. Occasionally a mosquito bite causes a large area of swelling, soreness and redness. This type of reaction, most common in children, is sometimes referred to as skeeter syndrome.

Bites from mosquitoes carrying certain viruses or parasites can cause severe illness. Infected mosquitoes in many parts of the world transmit West Nile virus to humans. Other mosquito-borne infections include yellow fever, malaria and some types of brain infection (encephalitis).

Symptoms

Mosquito bite signs include:

A puffy, white and reddish bump that appears a few minutes after the bite

A hard, itchy, reddish-brown bump, or multiple bumps, appearing a day or so after the bite or bites

Small blisters instead of hard bumps

Dark spots that look like bruises

More-severe reactions may be experienced by children, adults not previously exposed to the type of mosquito that bit them, and people with immune system disorders. In these people, mosquito bites sometimes trigger:

A large area of swelling and redness

Low-grade fever

Hives

Swollen lymph nodes

Children are more likely to develop a severe reaction than are adults, because many adults have had mosquito bites throughout their lives and become desensitized.

When to see a doctor

If mosquito bites seem to be associated with more-serious warning signs — such as fever, headache, body aches and signs of infection — contact your doctor.

Causes

Mosquito bites are caused by female mosquitoes feeding on your blood. Female mosquitoes have a mouthpart made to pierce skin and siphon off blood. Males lack this blood-sucking ability because they don't produce eggs and so have no need for protein in blood.

As a biting mosquito fills itself with blood, it injects saliva into your skin. Proteins in the saliva trigger a mild immune system reaction that results in the characteristic itching and bump.

Mosquitoes select their victims by evaluating scent, exhaled carbon dioxide and the chemicals in a person's sweat.

Complications

Scratching bites can lead to infection.

Mosquitoes can carry certain diseases, such as West Nile virus, malaria, yellow fever and dengue fever. The mosquito obtains a virus or parasite by biting an infected person or animal. Then, when biting you, the mosquito can transfer that virus or parasite to you through its saliva. West Nile and encephalitis viruses are found in the United States. Dengue fever has been reported in several southern states and Hawaii. Other diseases, such as malaria and yellow fever, are far more common in tropical areas of the world.

Prevention

You can take several steps to protect yourself from mosquito bites.

Avoid and exclude mosquitoes

Limit exposure to mosquitoes by:

Avoiding outdoor activities when they're most active, dusk to dawn

Repairing any tears in the screens on your windows, doors and camping gear

Using mosquito netting over strollers and cribs or when sleeping outdoors

Use insect repellent

The most effective insect repellents in the United States include one of three active ingredients:

DEET

Icaridin (also called picaridin)

Oil of lemon eucalyptus (a plant-based compound)

These repellents temporarily repel mosquitoes and ticks. DEET may offer longer lasting protection. Whichever product you choose, read the label before you apply it. If you're using a spray repellent, apply it outdoors and away from food.

If you're also using sunscreen, put it on first, about 20 minutes before applying the repellent. Avoid products that combine sunscreen and repellent, because you'll likely need to reapply sunscreen more often than repellent. And it's better to use only as much repellent as you need.

Used according to package directions, these products are generally safe for children and adults, with a few exceptions:

Don't use DEET-containing products on infants younger than 2 months.

Don't let young children get DEET or icaridin-containing products on their hands or faces.

Don't use oil of lemon eucalyptus on children under age 3 years.

Don't apply repellent under clothing.

Don't apply repellent over sunburns, cuts, wounds or rashes.

When you go indoors, wash with soap and water to remove any remaining repellent.

Treat clothing and outdoor gear

Permethrin is an insecticide and insect repellent used for additional protection. This product is applied to clothing and outdoor gear, not skin. Check the product label for specific application instructions. Some sporting goods stores sell clothing pretreated with permethrin.

Use protective clothing and gear

Weather permitting, wear:

Long sleeves

Socks and closed-toe shoes

Long pants, possibly tucked into the tops of your socks

Light colors

A hat that protects your ears and neck or one with mosquito netting that covers your face

Take preventive medication

If you tend to have large or severe reactions to mosquito bites (skeeter syndrome), consider taking a nondrowsy, nonprescription antihistamine when you know you'll be exposed to mosquitoes.

Reduce mosquitoes around your home

Eliminate standing water, which mosquitoes need to breed. To keep your house and yard free of mosquito pools: