Your daily SPF just got backup in the battle against skin cancer.

New research suggests a cheap, over-the-counter supplement may help protect against the disease — with benefits showing up in as little as a month.

Better yet, scientists found the vitamin cuts the risk of recurrence by more than half in people who have previously received a positive diagnosis.

The findings back up what dermatologists have been telling skin cancer survivors for a decade — take nicotinamide, a form of vitamin B3.

The advice stems from a 2015 clinical trial of 386 patients, which found fewer new skin cancers in those taking the supplement.

But verifying those results on a larger scale has been difficult, since nicotinamide can be purchased without a prescription, leaving no record in patients’ medical files.

To get around this, researchers tapped the Veterans Affairs Corporate Data Warehouse, where nicotinamide use is officially tracked.

They compared more than 12,000 patients taking 500 mg twice daily for at least a month with over 21,000 who didn’t.

Their focus: cases of basal cell carcinoma and cutaneous squamous cell carcinoma — two common types of non-melanoma skin cancer.

The researchers found that, on average, patients taking nicotinamide had a 14% lower risk of developing skin cancer compared to those who didn’t.

“The greatest impact was seen in squamous cell carcinoma, where risk dropped by more than 20%,” Dr. Yousuf Mohammed, research leader at the Frazer Institute, University of Queensland, who wasn’t involved in the study, said in a statement.

But the real headline? For those with a history of skin cancer, starting the supplement after their first case slashed the risk of recurrence by a whopping 54%.

That protective effect, however, declined sharply for those who had already battled multiple bouts of skin cancer before taking nicotinamide.

“There are no guidelines for when to start treatment with nicotinamide for skin cancer prevention in the general population,” Dr. Lee Wheless, assistant professor of Dermatology and Medicine at Vanderbilt University Medical Center and corresponding author of the study, said in a press release. 

“These results would really shift our practice from starting it once patients have developed numerous skin cancers to starting it earlier,” he added. 

Scientists are still figuring out exactly how nicotinamide fights skin cancer, but past research shows it helps cells repair DNA damaged by UV rays and dulls some of the immune-suppressing effects of sunlight.

“I am going to be more rigorous in recommending it to patients, especially patients who are having their first skin cancer,” Sarah Arron, a dermatologist, told NPR. “I think the benefit is strongest if we start it early.”

When buying the supplement, she recommends choosing the form that ends with “amide” — nicotinamide — rather than niacin (nicotinic acid), another type of vitamin B3 that doesn’t offer the same benefits.

Generally, nicotinamide is well-tolerated at normal doses. Side effects, if any, tend to be mild, such as nausea, diarrhea, headaches or fatigue.

“For clinicians, the appeal of nicotinamide lies in its accessibility, safety and tolerability,” Mohammed said. 

Because this study looked at veterans’ health records, the authors warned that the findings might not apply to women or younger people, and said a randomized clinical trial is still needed to confirm the results.

Each year, 5.4 million basal and squamous cell skin cancers are diagnosed in the US, and cases are rising, according to the American Cancer Society.

While nicotinamide may be a handy new weapon against skin cancer, experts say it’s no excuse to skip sunscreen and other sun-smart habits.