Americans are being warned to avoid squirrels after photos online showed the animals with “swollen faces, wart-like growths, and oozing sores.” The disturbing images, shared on Reddit and Facebook, sparked alarm among animal lovers.

Experts identified the illness as squirrel pox, or squirrel fibromatosis, a virus that causes tumor-like growths. Wildlife biologist Shevenell Webb explained that while it looks frightening, “it will run its course in time,” stressing that the disease is part of the animal’s natural ecology.

Though not always fatal, the virus can make squirrels weak by interfering with eating and movement. This leaves them more vulnerable to predators, which is why sick squirrels are often spotted in neighborhoods.

Experts caution against trying to capture or care for infected animals. Handling wildlife can be dangerous for both people and squirrels, causing stress or injury.

The safest approach is to observe from a distance and, if sick squirrels are common in one area, contact local wildlife services. While unsettling, squirrel pox is natural—“awareness and caution are key,” experts say.