evidence: It’s also perfectly fine to wear a hat and sunglasses to protect your face and eyes while exposing other parts of your body. Since the head is a small part of the body, it will only produce a small amount of vitamin D. [...] In fact, some studies estimate that sunscreen of SPF 30 or more reduces vitamin D production in the body by about 95–98% ( [...] SummaryIn theory, wearing sunscreen may reduce the ability to produce vitamin D, but short-term studies have shown it has little or no impact on blood levels. That said, it’s unclear whether frequently wearing sunscreen reduces your vitamin D levels in the long term.