How We Tested

Best of the Year arranged for DefenAge Skincare to ship the serum directly to 11 evaluators. Consumer testers, all over age 40, used the product for at least four weeks, allowing them to assess its immediate application and sensory experience as well as any changes they observed with continued use. They evaluated the serum’s texture, application, absorption, compatibility with their routines and overall performance.

Expert review included a dermatologist, two judges with cosmetic formulation and innovation background who assessed product’s ingredients, marketing claims and overall performance. Two additional judges with category expertise also used the serum on their own skin and assessed its performance from their perspectives. Sustainability judges reviewed the relevant environmental claims and materials. A packaging specialist conducted a detailed assessment of both primary and secondary packaging, delivery system and accompanying inserts. The Best of the Year analysts and editors also used the serum and reviewed the entry along with the supporting materials.

What Experts and Consumer Testers Said

Our experts and testers were especially taken with how the serum feels on skin. One skincare expert said, “It sinks readily into the skin and leaves it feeling exceptionally smooth, soft and almost velvety. After my first overnight use, my face appeared plumper, and I experienced no irritation.” Our cosmetic chemist judge agreed: “This serum feels amazing on the skin... Luxurious. The texture made me want to use it often.”

"It sinks readily into the skin and leaves it feeling exceptionally smooth, soft and almost velvety. After my first overnight use, my face appeared plumper, and I experienced no irritation." -Best of the Year Judge & Beauty Category Expert

One dermatologist judge brought a longer-term perspective, having used the brand for years professionally. “Works very well. Good long-term results, not irritating,” she told us, adding that while it is pricey, its “all-in-one” approach helps make the cost worthwhile. Another scientist praised the formula as “aesthetically pleasing, lightweight with easy rub in and absorption, soft skin finish.”

"Works very well. Good long term results, not irritating." -Best of the Year Judge & Dermatologist

"Formula is aesthetically pleasing, lightweight with easy rub in and absorption, soft skin finish." -Best of the Year Judge & Beauty Category Expert

Our consumer testers had similarly positive things to say about everyday use: “It absorbs quickly, and it's not sticky or shiny”, said one. After several weeks, she also saw changes in her skin: “Within a couple of weeks, I noticed my skin seemed more youthful, a little smoother, a little plumper. And I can see the results are continuing, the longer I use it.” She also felt the serum could replace several products she might otherwise layer, saving time in her routine.

"Within a couple of weeks, I noticed my skin seemed more youthful, a little smoother, a little plumper. And I can see the results are continuing, the longer I use it." -Best of the Year Consumer Tester

Best of the Year Bottom Line

DefenAge 8-in-1 BioSerum pairs serious skincare science with something just as important: a formula people actually enjoy using. Our experts and testers loved its silky, fast-absorbing feel and saw smoother, plumper-looking skin without the irritation often associated with retinol. No question, it’s an investment, but a worthy one based on our testing, and the bigger changes may take time, but for those looking to tackle multiple signs of aging in one gentle, well-formulated serum, it delivers a lot in one bottle.

Why Trust Us?

The Best of the Year Media team comprises award-winning editors, analysts, subject-matter experts and consumer specialists who have spent their careers helping people make smarter, more confident decisions. With deep expertise across consumer lifestyle categories, our team brings decades of experience evaluating products, brands and services. Our recommendations are grounded in rigorous evaluation combined with expert judgment and consumer insights, giving readers trusted guidance on products, services, and experiences worth bringing into their lives.

P.S. We use affiliate shopping links where possible. We may make a few dollars if you click them. It’s one of the reasons we're able to give you a calmer site experience, with fewer ads and distracting pop-ups.