Glutathione capsules lightened sun-exposed skin only, and not for long
At 250 to 500mg a day for four to twelve weeks, forearm and facial skin measured lighter than placebo while covered skin did not change. The lightening fades on stopping.
What the study found
Swallowed glutathione lightens only the skin the sun already reached
The effect stops where the sunlight stopped. At 250 to 500mg of glutathione a day for four to twelve weeks, sun-exposed forearm and facial skin measured lighter than placebo, while skin kept covered did not change. The lightening fades once people stop taking it.
The caveat · Nobody measured glutathione in blood
The trials ran 46 to 124 people over four to twelve weeks. In the twelve-week trial the change concentrated in participants over 40 rather than spreading across the group, and in the four-week trial the count of sun spots never moved even as the melanin reading did. No trial measured glutathione in the blood, so nothing rules out the capsules working through something other than the mechanism the marketing assumes. Participants were mostly Asian adults already seeking lighter skin.
What we don't know
Nobody disputes which way swallowed glutathione pushes skin tone. What is open is whether a handful of small, short trials is enough to call it settled, and reviews split on how much of that evidence to admit.