Happiness is contagious, but so are colds and the flu. When your kids return to school this fall, they’re returning to one of the happiest and most contagious places in their world.

“Schools inherently foster the transmission of infections,” according to a study in the American Journal of Public Health. That’s due to group settings where kids are in close contact and share supplies or equipment. Add to that food, high-fives, and plenty of other everyday activities, and you have a recipe for spreading germs.

The classroom, playground, and school bathrooms are just a few of the many places where students can catch contagions. Here are a few more sources for illness you may be unaware of—and how your child can avoid getting sick at school.

Gym equipment

According to the New York Times, in 2007, a rash of nasty infections started cropping up across the country, and the culprit was found to be MRSA, more commonly known as staph—a bacteria that is resistant to many antibiotics.

Young children are susceptible to catching skin infections that arise from this bacteria, and it can live in warm, damp environments such as wet gym towels or gym equipment that hasn’t been wiped down.

For younger kids, make sure they know the importance of washing their hands often. If they have any open sores, make sure they’re covered. For older kids who may be in a more labor-intensive gym class, tell them to wipe down their the gym equipment before using it, and—if showering after—to use their own towels, razors, and sandals.

For both age groups, talk to school officials so you can be certain that they’re wiping down and disinfecting commonly used surfaces frequently.

The school bus

Your children don’t have to be sitting behind an idling bus to feel the effects of exhaust fumes. In fact, exhaust in the surrounding air can be drawn in by the building’s ventilation system, bringing toxins into the school.

If fumes from the bus start to pollute the air in a school’s classrooms or hallways, students and staff members could start displaying a number of uncomfortable symptoms, including asthma and respiratory infection. Be alert to any coughing or wheezing symptoms your child starts exhibiting and see if his classroom is situated near the parking lot.

Heating/AC and the ventilation system

This all-important system of tubes running throughout the school can have plenty of problems. If AC or heating units get blocked by a janitor’s trashcan or a student’s backpack, it can reduce airflow, which leads to one or more potential conditions that could have your kid feeling under the weather.

First, poor airflow means that the air being circulated in the school environment is recycled more slowly, meaning it’s generally dirtier and more stale (think about the air on an airplane). Besides being uncomfortable, poorly circulated air makes it easier for germs to spread from person to person. Second, bad airflow can lead to the condensation of water within the ventilation system, which in turn leads to the development of mold. Mold irritates many people’s allergies, causing red or itchy eyes, rash, coughing, and more. Some molds produce symptoms even in people without allergies, so if your child is sneezing or itching even when they don’t typically experience hay fever, mold could be the culprit.

Though all these precautions are important, it’s impossible for supervisors—let alone students—to be on guard for all of these potential risks. Personal and environmental hygiene can only go so far. All students need immunizations and regular checkups to stay healthy.

Take heart

Despite these germy details, it’s important to note that there is another way of looking at the issue of our children and germs. A theory called the hygiene hypothesis supports the idea that a baby’s immune system must be educated in order to function properly for the rest of his or her life. History has shown us that over time, as a society moves from third-world conditions to more sanitary living conditions, the rates of autoimmune and allergic disorders increase. In the United States, since the 1950s, rates of multiple sclerosis, Crohn’s disease, type 1 diabetes, hay fever, food allergies and asthma have soared by over 300%. This hypothesis suggests that extremely clean environments found in the developed world can be “too clean” to provide the necessary exposure to germs babies need to “educate” the immune system.

So this fall don’t let contagious bugs or bad air quality get in the way of your child’s education. If your child does get sick—don’t panic—there is some evidence to suggest it may be helpful for his or her future health.