Schools are a breeding ground for germs – they're forever plagued by illness outbreaks that potentially disrupt student learning and facility operations. We know that surface disinfection is one key way to break the germ cycle, providing peace of mind that killing germs on surfaces means healthier school facilities. But have we thought enough about what is left behind after we kill the germs, and are we confident it's not another risk to our students and staff?
Whether the goal is to disinfect a restroom or a child's desk, when it comes to cleaning surfaces, it's important to consider what gets left behind by the materials and products you use. Surface disinfectants are specially designed to kill bacteria, and most disinfectants contain an active chemical that specifically works to destroy germs that can cause illness. You deposit germ-killing chemicals every time you spray or wipe a surface with these products. We talk a lot about "dwell time" when it comes to disinfectants – this is the amount of time the product needs to be on the surface to kill key germs – and that time typically ranges from 30 seconds to up to 10 minutes. We don't frequently ask, "What happens to the chemical after it kills the germs? "
Many Common Disinfectant Products Leave Unwanted Residues Behind
One of the potentially unknown dangers of some chemical-based disinfectant products is the residue their active ingredients may leave behind. A chemical residue is what's left behind on a surface after the product is used. Just as a paper towel can leave bits of paper residue on a surface, so can a disinfectant spray or wipe. We certainly don't want to replace surface germs with chemicals. But not all disinfectant chemicals produce unwanted surface residues. Whether or not a chemical remains behind on surfaces depends on its chemistry:
- Some chemicals – like ethanol or isopropanol alcohols – evaporate quickly, so they do not leave a chemical residue behind.
- Other types of chemicals are not very stable (i.e., don't last long) on surfaces and quickly "break apart" after killing germs. One example is hydrogen peroxide, which breaks down into naturally occurring materials: water and oxygen.
- Many common disinfectant chemicals have electric "charges" which can help them stick to surfaces, similar to static. This means they may linger on surfaces for extended periods of time and may actually require rinsing and wiping to physically remove them from surfaces (which is indicated on the product's label).
How Common Are Disinfectant Residues in Schools?
Many schools use the same cleaning and disinfecting products every day – and potentially for years, so residues can easily build up on the surfaces, depending on the active ingredient. We recently partnered with leading toxicologists and environmental health experts to understand disinfectant chemical exposures in schools. Together, we conducted a research study in a school that had been using a common disinfectant for many years and had increased its use – as most schools did – during the pandemic. We wanted to understand how much chemical residue was left on surfaces between product uses. When desks were sampled on days when the product wasn't used, we were able to measure the chemical on more than 90% of surfaces sampled, left over from cleaning the day before!1 We also showed that chemical residues on hard surfaces like desks were easily transferred to hands simply by touching their surfaces!2
Why Are Chemical Residues Bad?
Residues like the ones found in this study can create short- and long-term issues, which may include:
- Damage to hard surfaces. Visible signs of damage from residues include surface material corrosion and discoloration.
- Buildup of dirt or grime (and even germs). Chemical residues often make surfaces sticky, so it's easier for dirt and grime to pile on. Also, surfaces often need to be cleaned first for the disinfectant to work, so if there is a lot of buildup on the surface, your disinfectant may be unable to cut through the grime to reach and kill the germs.
- Skin irritation or allergy. In school settings, kids' hands and forearms are in close contact with desks, handrails, and other surfaces on which disinfectants are used. Skin that repeatedly comes in contact with chemical residues for extended periods of time can become irritated, or skin allergies like eczema can be triggered.
- Problems with indoor air quality. Surface residues may also aggravate allergies or other sensitivities such as asthma.
Why Are Kids More at Risk from Chemical Residues?
Children's bodies are smaller and still developing. Compared to adults, they breathe more air and have more skin to potentially absorb chemicals. Importantly, kids also act differently – touching more surfaces and "hand-to-mouth" behavior – which makes them more likely to ingest what they touch. Combining these factors with the amount of time spent in school environments every day, they're especially vulnerable to the effects of chemicals in these spaces.
How to Avoid Disinfectant Chemical Residues in Your Facility?
Obviously, we don't want to bring harsh chemicals that may linger into our schools. With the safety of our students and staff front of mind, we are already careful to avoid using disinfectants around children. The Environmental Protection Agency (EPA) says that disinfectants should never be used by children and should be kept out of children's reach.3 To help keep them safe, we also want to ensure we are not saturating our hard surfaces with chemicals that may be touched for hours each day, potentially exposing kids and staff to more risk. Here are 4 steps to help avoid chemical residues:
- Look for Surface "Signs." Residue is often unseen at the onset, so any change in surface feel, texture, or signs of corrosion is often an indication. Do surfaces feel sticky, tacky, slimy, or greasy, even if they appear clean? Lingering odors are also often a sign of residues. One school district was made aware of improper use of chemical disinfectant and residues present due to strong odors and discolored clothing of students.4
- Follow Disinfectant Label Instructions. One of the easiest ways to eliminate residues is to ensure directions are followed for proper application. Spot the difference between "rinse" and "non-rinse" cleaners. (For more on this, read my colleague's blog post.)
- Swap-Out Chemicals. Consider alternating the usage of disinfectant products with different chemicals to avoid buildup. Make sure you never mix disinfectant chemicals!
- Choose Lower-Toxicity Chemicals. Choosing the best disinfectants for an educational facility means doing your homework. Read the ingredients list carefully and note potential dangers such as lung or skin irritation or allergy. Consider lower toxicity or "green" cleaning and disinfecting programs. Consult resources like Healthy Green Schools & Colleges Standard and EPA's Safer Choice Standards EPA's Safer Choice Standards for more information.
For more information on this topic, read my other blog, "What Chemicals Are In Your School's Cleaning Products?"
The PURELL® brand has already taken all of this into consideration in our carefully formulated surface products. Effective and worry-free, our surface spray and wipes have earned the EPA's lowest toxicity rating. For more information, visit GOJO.com/surfaces.