The fountain of youth might already be sitting in your bathroom cabinet. A new study found that all-year round use of sunscreen significantly slowed the aging of skin caused by the sun's ultraviolet rays.

The study published in Annals of Internal Medicine found that when adults regularly used broad spectrum sunscreen - which protects against both ultraviolet B and ultraviolet A rays --  they were less likely to show increased wrinkling over a four-and-a-half-year period than adults who used sunscreen less often.

"We weren't surprised by the findings, but we now have the science to back it up," says Adele Green, a senior scientist at the Queensland Institute of Medical Research and lead author of the randomized, controlled trial -- considered the gold standard of scientific research -- published Monday in Annals of Internal Medicine, in an email to NBC News.

Australian researchers who conducted the study randomly assigned 903 adults, 24 to 55 years old, to use sunscreen (SPF 15+) every day or to use it whenever they wanted. Participants in the daily-use group applied sunscreen every morning to their head, neck, arms and hands and reapplied it after heavy sweating or bathing and whenever they spent more than a few hours outside, according to the study.

The researchers conducted skin examinations at the beginning of the study and again 4 and a half years late. The adults using daily sunscreen were 24 percent less likely to show increased aging, according to the study. Regardless of sex, age, skin color, occupation, skin cancer history, weight and smoking, everyone benefitted from daily sunscreen use

A sunscreen with an SPF 15 blocks about 94 percent of ultraviolet B rays, which are responsible for sunburn, while one with an SPF of 40 filters about 97.5 percent.

"The more important issue is applying the sunscreen well and reapplying it often," says Green.

The broad spectrum sunscreen in the Australian study protected against both ultraviolet B rays and ultraviolet A rays, which penetrate deeper and cause skin damage. Dermatologists now think that both types of rays cause the skin to age.