14 Causes of Impetigo

2. Insect Bite

An insect bite can create a small break in the skin, forming an entry point for bacteria. Common biting insects include mosquitoes, fleas, and mites. Their bites usually cause itching rather than pain, which increases the urge to scratch.

Scratching the bite can tear the skin further, making the opening larger and easier for bacteria to enter. Bacteria that cause impetigo, such as strep or staph, often live on the skin without causing harm. Once the skin barrier is broken, these bacteria can move into deeper layers and begin to multiply, leading to a superficial skin infection.

As the infection progresses, the area may become red and develop small blisters or sores that can burst and form crusts. Children are more likely to scratch bites, especially in warm, humid weather, which allows bacteria to grow faster and increases the risk of infection.

3. Skin Injury

Skin injury is one of the most common causes of impetigo. When the skin barrier breaks, bacteria can enter and begin to grow. Even small cuts, scrapes, burns, or surface irritation can weaken the skin’s protective layer and create a path for infection. If the injured skin is not cleaned and protected, bacteria can multiply and spread more easily.

Skin conditions that cause itching further raise the risk. Scratching eczema, chickenpox, or other rashes damages the skin and allows bacteria to enter. Impetigo usually starts at an injury site, initially appearing red or irritated, and then developing fluid-filled blisters or honey-colored crusts as it worsens.

Minor injuries around the nose, mouth, hands, or legs are common starting points because these areas are frequently exposed and touched. Warm, humid conditions and frequent skin contact with others can further increase the chance that bacteria will spread and cause infection in injured skin.

4. Surface Contact

Surface contact spreads impetigo when bacteria move from one person’s skin to another. This often happens through direct touch, such as holding hands, hugging, or playing contact sports. Young children face a higher risk because close physical contact is common during play and hygiene habits are still developing.

Bacteria can also spread through shared objects and surfaces. When a person with impetigo touches toys, towels, clothing, bedding, or sports equipment, bacteria may remain on these items for a short time. Another person who uses the same item can transfer the bacteria to their own skin, especially if items are shared frequently without cleaning.

Once on the skin, infection is more likely when there are small breaks in the surface. Cuts, scrapes, insect bites, or eczema create openings that allow bacteria to enter. Regular handwashing, avoiding shared personal items, and cleaning commonly touched surfaces can help reduce the spread of impetigo.

5. Animal Bite

An animal bite can break the skin and damage its protective barrier. Even small puncture wounds or scratches can create openings that allow bacteria to enter the top layers of the skin. Germs such as staph or strep can then begin to grow and lead to impetigo, especially when the wound is not cleaned right away.

Both pets and wild animals can cause bites. Dog or cat bites, as well as scratches that break the skin, increase the risk of infection because animal mouths and claws naturally carry bacteria. Deep puncture wounds are especially risky because bacteria can become trapped beneath the skin surface. As bacteria multiply, the area may become red, warm, and sore. Within days, small fluid-filled or pus-filled blisters can form.

These blisters may burst and leave a yellow, crusted surface, which is a common sign of impetigo. Swelling or increasing tenderness may also appear as the infection spreads. Children face a higher risk because they often play closely with animals and may not report bites or scratches right away.

6. Infection by Streptococcus

Infection by Streptococcus bacteria is a common cause of impetigo. The type most often involved is group A Streptococcus, which infects the top layer of the skin and spreads easily through close contact, especially in warm, crowded environments.

The bacteria usually enters through a break in the skin, such as cuts, scrapes, insect bites, eczema, or small cracks that may not be easily seen. Poor hygiene and frequent scratching increase the chance that bacteria move deeper into these openings. Once inside the skin, the bacteria multiply quickly and trigger a local skin infection.

This growth leads to red sores that may open and form a yellow, crusted surface, which is a classic sign of impetigo. These sores often appear around the nose and mouth but can spread to other areas of the body, especially skin that is frequently touched or irritated.

The infection can also spread through direct contact with the fluid from the sores or by sharing personal items such as towels, clothing, or bedding. Because the bacteria spread easily from skin to skin, outbreaks are more likely in places where children gather closely, such as schools or daycare centers.

7. Crowded Conditions

Crowded living spaces raise the risk of impetigo by increasing frequent skin contact. When many people share small areas, bacteria can move more easily from one person to another. Impetigo spreads through direct skin contact and through shared items that touch the skin. These include towels, bedding, clothing, and sports gear.

In crowded settings, people are more likely to share these items without realizing the risk. Children face higher risk because they often play closely and may not wash their hands well. Touching sores and then touching other people or objects allows bacteria to spread further.

Warm and humid conditions add to the problem. Sweat and moisture soften the skin and support bacterial growth, making infection more likely. Crowded conditions make it difficult to separate someone who has the infection or to keep personal items separate, allowing bacteria to continue spreading within the group.

Sharing clothing can spread the bacteria that cause impetigo. These bacteria often live on the skin or inside the nose without causing problems. When a person has impetigo, bacteria from open sores or fluid-filled blisters can transfer onto fabric.

Clothing that touches infected skin can then carry bacteria to another person. This includes shirts, pants, pajamas, socks, underwear, and school or sports uniforms. Items that rub against the face, arms, or legs pose a higher risk, since impetigo often affects these areas.

Children face a higher risk because they commonly share hoodies, jackets, sports gear, and costumes. In schools or daycare settings, clothing may be mixed by mistake. If items are not washed between uses, bacteria can survive long enough to infect another child. Skin irritation increases the risk further. Tight or rough clothing can cause friction and small breaks in the skin, making it easier for bacteria to enter.

9. Change of Seasons

Changes in season can raise the risk of impetigo by affecting both the skin and bacterial growth. Warm and humid weather allows bacteria to multiply more easily on the skin, which is why cases often increase during spring and summer, especially in children.

During these months, outdoor play also raises the chance of small cuts, insect bites, and scratches that can let bacteria enter the skin. Sweating and frequent skin contact during sports or play can also keep the skin moist, creating conditions that allow bacteria to grow more easily. Cold weather can increase risk in a different way.

Dry winter air can cause the skin to crack, particularly on the hands, lips, and face. These breaks weaken the skin’s protective barrier and make it easier for bacteria such as Staphylococcus or Streptococcus to cause infection. Seasonal allergies increase risk by causing itching and scratching that break the skin and allow bacteria to enter.

Close-contact sports can spread impetigo from one person to another. Activities such as wrestling, football, basketball, and rugby involve frequent skin-to-skin contact, allowing bacteria to move easily from infected skin to another person. Shared equipment also increases risk. Mats, helmets, towels, uniforms, and other gear can carry bacteria when not cleaned or disinfected between uses, allowing infection to spread within teams.

Skin injuries are common during sports. Minor cuts, turf burns, scrapes, and insect bites create small breaks in the skin, making it easier for bacteria such as Staphylococcus aureus or group A Streptococcus to enter and cause infection.

Sweating adds to the problem. Warm, moist skin supports bacterial growth, while crowded locker rooms and close team settings increase exposure. Poor ventilation and delayed showering after practice can further raise the risk. Covering cuts or abrasions before activity and avoiding play when skin infections are present can help limit spread among teammates.

11. Diabetes

Diabetes raises the risk of impetigo by affecting both the immune system and the skin. Persistently high blood sugar levels can weaken immune defenses, making it easier for common bacteria such as Staphylococcus or Streptococcus to cause skin infections.

High glucose levels can also create conditions that allow bacteria to grow more easily on the skin. Diabetes also changes the condition of the skin. Reduced moisture and slower cell repair can make skin dry, thin, or fragile, delaying healing of cuts or scrapes. Even small breaks, including cracks, blisters, or insect bites, can allow bacteria to enter and multiply.

Poor blood flow adds to this risk. Damage to small blood vessels limits oxygen and nutrient delivery to the skin, slowing healing and reducing the body’s ability to clear infection once bacteria enter.

12. Dialysis

Dialysis can raise the risk of skin infections, including impetigo, by affecting immune function and skin integrity. Chronic kidney disease and dialysis both place ongoing stress on the immune system, making it harder for the body to fight bacteria that normally live on the skin. Impetigo develops when bacteria enter through a break in the skin.

People on dialysis often experience dry, itchy, or fragile skin, which increases scratching and the chance of small cuts or cracks. These openings allow bacteria such as Staphylococcus aureus or Streptococcus pyogenes to enter and multiply. Hemodialysis requires repeated needle insertion into the same access site, such as a fistula or graft.

This repeated puncturing can irritate the skin and slow healing over time. Even with strict infection control, dialysis patients spend many hours each week in medical settings where frequent contact with equipment and shared surfaces increases exposure to germs.

13. Skin Issues

Skin problems raise the risk of impetigo by damaging the skin’s outer protective layer. When this barrier breaks, bacteria can enter and begin to grow. Even tiny cracks or areas of irritation can become entry points for infection.

Conditions that cause itching and inflammation are common triggers. Eczema leads to dry, itchy skin, and repeated scratching breaks the skin surface, creating small wounds where bacteria can spread easily.

Contact dermatitis also weakens the skin barrier. Reactions to soaps, plants, metals, or other irritants can cause rashes that blister, peel, or crack, reducing the skin’s ability to protect against bacteria.

Insect bites and minor rashes create similar risks. Children often scratch these areas, and repeated scratching can leave the skin raw and more vulnerable to infection. Warm or humid conditions can further worsen irritation and bacterial growth.

Fungal skin infections may further increase risk. Scaling, redness, and cracks in skin folds or between toes provide openings where bacteria can grow. Other chronic skin conditions, such as psoriasis, can form thick, dry patches that split open.

14. Complications

Impetigo is usually mild, but complications can develop in some cases. These problems are uncommon, yet they may occur when the infection is not treated promptly, spreads, or affects people with weaker immune systems.

If the infection moves beyond the surface of the skin, it can lead to cellulitis, an infection of the deeper skin and underlying tissue. The affected area may become red, swollen, warm, and painful. Fever, chills, or a general feeling of illness may also occur, and medical treatment is required to prevent further spread.

In rare cases, the bacteria can trigger a kidney condition called post-streptococcal glomerulonephritis. This complication may appear one to two weeks after the skin sores have healed and can cause dark or cola-colored urine, swelling in the face or legs, reduced urine output, and high blood pressure.

Other possible complications include ecthyma, a more severe form of impetigo in which sores extend deeper below the top layer of skin. These deeper ulcers heal more slowly and may leave permanent scars.