Is 20% vitamin C too strong for beginners?

It is on the high end. Start every other day and patch test first, especially if your skin is sensitive or dry.

Can I use it with retinol or niacinamide?

Yes, but apply vitamin C in the morning and retinol at night to reduce irritation. Niacinamide layers fine with it for most people.

Why did my serum turn yellow?

L-ascorbic acid oxidizes when exposed to light and air. A yellow tint means it is losing potency; store it cool and dark and use it within a few months of opening.

Is it good for oily skin?

Yes. The light, fast-absorbing formula is made for normal to oily skin and does not leave a heavy film.

How does it compare to the 15% version?

The 20% delivers a higher acid dose for faster brightening but is more likely to sting. The 15% suits reactive or first-time vitamin C users.

The best new price was $59.99 at Walmart as of November 5, 2026. Vitamin C serums often dip during seasonal sales, so compare across the three stores listing it.