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).

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.

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.

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.

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:

• Unclog roof gutters.
• Empty children's wading pools at least once a week, and preferably more often.
• Change water in birdbaths at least weekly.
• Get rid of old tires in your yard.
• Empty outdoor flower pots regularly or store them upside down so that they can't collect water.
• Drain your fire pit if water collects there.

Doctors can usually identify mosquito bites by sight.

The red, itchy, painful swelling referred to as skeeter syndrome is sometimes mistaken for a secondary bacterial infection brought on by scratching and broken skin. Skeeter syndrome is actually the result of an allergic reaction to proteins in mosquito saliva. There's no simple blood test to detect mosquito antibodies in blood, so mosquito allergy is diagnosed by determining whether the large, red areas of swelling and itching occurred after you were bitten by mosquitoes.

Most mosquito bites stop itching and heal on their own in a few days. These self-care tips may make you more comfortable.

• Apply a lotion, cream or paste. Putting calamine lotion or nonprescription hydrocortisone cream on the bite can help ease the itch. Or try dabbing the bite with a paste made of baking soda and water. Reapply several times daily until your symptoms go away.
• Apply a cool compress. Try soothing the bite by applying a cold pack or a cool, moist cloth for a few minutes.
• Take an oral antihistamine. For stronger reactions, try taking a nonprescription antihistamine (Benadryl, Chlor-Trimeton, others).

You won't need to see your doctor for a mosquito bite, unless you develop a fever or other signs and symptoms that sometimes develop after such bites.

Here's some information to help you get ready for your appointment.

What you can do

Before your appointment make a list of:

• Symptoms you've been having and for how long
• All medications, vitamins and supplements you take, including the doses
• Questions to ask your doctor

If you're having signs and symptoms you think might be related to a mosquito bite, some basic questions to ask your doctor include:

• What can I do to stop the itch?
• Is the area around my mosquito bite infected?
• Does the medication you're prescribing have any side effects?
• How will I know if I need additional care?

What you can do in the meantime

If itching is a problem, an over-the-counter antihistamine (Benadryl, Chlor-Trimeton, others) may help.