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.

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.