Now there's a new tool that's helping doctors answer that question right in their office.
After having skin cancer three times Amanda Bosca wants to make sure the two new dots on her face are not cancer.
To help figure it out fast, her doctor is using a new device called the Vivosight Scanner.
Using multi-beam laser technology, it creates an image on the monitor showing the layers of skin.
"Something like this allows us to quickly and non-invasively give people feedback about areas of concern," said Dr. Erin Gilbert.
Dr. Gilbert is a dermatologist at Gramercy Park Dermatology Associates which, according to makers of Vivosight, is the only practiced in the United States offering the new technology.
If topical creams are prescribed, she says the images can tell her if they're working. And the device may help patients like Amanda avoid a biopsy. Her new spots turned out to be benign cysts.
But that dreaded biopsy is still the gold standard for diagnosing skin cancer, and keep in mind this device is still new.
Dr. Gilbert explains how they know if they are missing something. "In the cases where we're using this diagnostically is where we're 95% to 100% certain what we're looking at," she said.
The accuracy depends on the doctor and it takes practice to interpret these images.
Vivosight can only see 2 mm into the skin and it is not useful for invasive skin cancers or melanoma
The device has been cleared by the FDA.
It is not covered by insurance, and Dr. Gilbert says she charges patients $275 to use it. Part of that fee goes to the medical practice, part of it goes to the company to pay for the use of the machine