Mosquitoes are insects that live all over the world. There are thousands of different species of mosquitoes; about 200 of those live in the United States.

Female mosquitoes bite animals and humans and drink a very small amount of their blood. They need protein and iron from blood to produce eggs. After drinking blood, they find some standing water and lay their eggs in it. The eggs hatch into larvae, then pupae, and then they become adult mosquitos. The males live for about a week to ten days, and the females can live up to several weeks. Some female mosquitoes can hibernate in the winter, and they can live for months.

Most mosquito bites are harmless, but there are times when they can be dangerous. The ways that mosquito bites can affect humans include:

• Causing itchy bumps, as an immune system response to the mosquito's saliva. This is the most common reaction. The bumps usually go away after a day or two.
• Causing allergic reactions, including blisters, large hives, and in rare cases, anaphylaxis. Anaphylaxis is a severe allergic reaction that affects the whole body. It is a medical emergency.
• Spreading diseases to humans. Some of these diseases can be serious. Many of them do not have any treatments, and only a few have vaccines to prevent them. These diseases are more of a problem in Africa and other tropical areas of the world, but more of them are spreading to the United States. One factor is climate change, which makes the conditions in some parts of the United States more favorable to certain types of mosquitoes. Other reasons include increased trade with, and travel to, tropical and subtropical areas.

Common diseases spread by mosquitoes include:

• Chikungunya, a viral infection that causes symptoms such as fever and severe joint pain. The symptoms usually last about a week, but for some, the joint pain may last for months. Most cases of chikungunya in the United States are in people who traveled to other countries. There have been a few cases where it has spread in the United States.
• Dengue, a viral infection that causes a high fever, headaches, joint and muscle pain, vomiting, and a rash. Most people get better within a few weeks. In some cases, it can become very severe, even life-threatening. Dengue is rare in the United States.
• Malaria, a parasitic disease that causes serious symptoms such as high fevers, shaking chills, and flu-like illness. It can be life-threatening, but there are drugs to treat it. Malaria is a major health problem in many tropical and subtropical areas of the world. Almost all cases of malaria in the United States are in people who traveled to other countries.
• West Nile Virus (WNV), a viral infection that often has no symptoms. In those that do have symptoms, they are usually mild, and include fever, headache, and nausea. In rare cases, the virus can enter the brain, and it can be life-threatening. WNV has spread across the continental United States.
• Zika Virus, a viral infection that often does not cause symptoms. One in five infected people do get symptoms, which are usually mild. They include a fever, rash, joint pain, and pink eye. Besides being spread by mosquitoes, Zika can spread from mother to baby during pregnancy and cause serious birth defects. It can also spread from one partner to another during sex. There have been a few outbreaks of Zika in the southern United States.

• Use an insect repellent when you go outdoors. Choose an Environmental Protection Agency (EPA)-registered insect repellent. They are evaluated to make sure they are safe and effective. Make sure that the repellant has one of these ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol. It is important to follow the instructions on the label.
• Cover up. Wear long sleeves, long pants, and socks when outdoors. Mosquitoes may bite through thin fabric, so spray thin clothes with an EPA-registered repellent like permethrin. Don't apply permethrin directly to skin.
• Mosquito-proof your home. Install or repair screens on windows and doors to keep mosquitoes out. Use air conditioning if you have it.
• Get rid of mosquito breeding sites. Regularly empty standing water from your house and yard. The water could be in flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, or birdbaths.
• If you plan to travel, get information about the areas you will be going to. Find out whether there is a risk of diseases from mosquitoes, and if so, whether there is a vaccine or medicine to prevent those diseases. See a health care provider familiar with travel medicine, ideally 4 to 6 weeks before your trip.