By now we all know we should wash our hands often to avoid getting sick, but experts say there could be health hazards lurking underneath our own fingernails. A leading biologist warns that bacteria thrive in the crevices under fingernails and the more area they have to grow, the greater the health risks.

“The longer the nail, the more surface area there is for microorganisms to adhere,” says Jeffrey Kaplan, a professor in the biology department at American University. “Studies have found 32 different bacteria and 28 different fungi underneath fingernails.

According to USA Today, Kaplan says it doesn’t matter if the long nails are real or artificial because no matter what the surface, the length makes it difficult to thoroughly clean and decontaminate. He adds that one study found MRSA, an antibiotic-resistant bacteria that could cause serious infection, underneath 50% of fingernail samples analyzed.

The bacteria or fungi living under your nails could cause nails to become disfigured, and the pathogens can find ways into your body to trigger sickness. In addition, the risk of transmitting the infection to more vulnerable individuals is possible, which is why healthcare workers are required to keep their fingernails trimmed.

A potentially lethal bacteria found under the fingernails of some nurses at the Children’s Hospital of Oklahoma was linked to the deaths of 16 babies in intensive care in 1997, reports WebMD. Centers for Disease Control and Prevention (CDC) researchers found a potentially lethal form of bacteria under the fingernails of two nurses there. One had long, natural fingernails and the second had long, fake nails.

And Kaplan says you can also transmit bacteria like staphylococcus into your own system by “scratching, nail-biting, nose-picking and finger-sucking.” 

The CDC says that fingernails should be kept short to reduce the spread of infections and the undersides should be cleaned frequently with soap and water. “Before clipping or grooming nails all equipment should be properly cleaned,” says the agency. “Sterilizing all equipment before use is especially important when nail tools are shared among a number of people.”