This 2020 human/rodent study investigated treating and preventing skin photodamage with sulforaphane:

“Alterations in NRF2 signaling have been implicated in aging and stress-induced skin pigmentation disorders in the skin and hair follicles. NRF2 signaling regulates transcriptional programs involved in adaption and survival of cells in the setting of oxidative stress, and oxidative stress occurs in the setting of photodamage.

[1^st human experiment with 14 subjects] Expression levels of NRF2 and its target heme-oxygenase-1 (HO-1) were evaluated by immunofluorescence (IF) in skin biopsies. Expression of NRF2 and HO-1 was significantly reduced in skin from individuals > 45 years old.

[2^nd human experiment with 7 different subjects] The left arm was chosen for treatment with BSE [broccoli sprout extract], as there is typically more photodamage on the left arm due to chronic sun exposure through the car window while driving in the US. A photoprotected area of skin on an upper inner arm was also treated.

Expression of total NRF2 and phosphorylated NRF2 (NRF2-P) by IF microscopy was detected at low baseline levels in photoprotected skin, suggesting some activity of the pathway, whereas the expression of total NRF2 and NRF2-P was undetectable in untreated photoexposed skin (Un). There was significantly elevated IF expression and fold change of IF signal of NRF2 and especially NRF2-P in SF [sulforaphane]-treated skin compared with Un skin in most individuals.

There was no evidence of increased total NRF2 or NRF2-P expression in SF-treated photoexposed skin in 2 individuals. There was also no significant improvement in mottled hyperpigmentation or difference in melanin deposition following SF treatment.

[Six mouse confirmation/exploratory studies] SF is known to have several non-NRF2–mediated targets, such as NF-κB and AP-1. However, our findings suggest that negative regulation of UV-mediated hyperpigmentation observed following SF treatment is occurring in an NRF2-dependent fashion:

• UVB+SF treatment resulted in more than a 50% decrease in skin pigmentation and melanin deposition, indicating that SF could prevent UVB-induced skin pigmentation.
• The therapeutic effect of SF on reducing UVB-induced skin pigmentation was dependent on keratinocyte-intrinsic IL-6 receptor α (IL-6Rα) signaling that upregulated NRF2, which led to inhibition of melanogenesis.

Our results provide direct in vivo evidence of how NRF2 is involved in response to oxidative stress associated with photodamage and chronic UV exposure. Treatment of human or mouse skin hyperpigmentation with SF provided the proof of concept for targeting the NRF2 pathway as a therapeutic intervention.”

https://insight.jci.org/articles/view/139342 “Pathogenic and therapeutic role for NRF2 signaling in ultraviolet light–induced skin pigmentation”

Didn’t understand the 2^nd experiment’s human dose of 5 nM sulforaphane. The lead author’s cited 2017 study Randomized, split-body, single-blinded clinical trial of topical broccoli sprout extract: Assessing the feasibility of its use in keratin-based disorders used “500 nmol of sulforaphane/mL.” Unless my math is off, the current study and previous study’s doses weren’t equivalent since 1 nM = 0.001 nmol/mL.

I’d like to know more about subjects who didn’t respond to topical sulforaphane treatment. What happened in their lives to make them dead to an evolutionarily-selected antioxidant and anti-inflammatory signaling pathway that influences many other internal environmental signals? Guess we’ll have to wait for:

“Further clinical studies with an increased number of human subjects, longer treatment regimens, and additional body sites are needed to further assess the long-term effects of NRF2 activation on photoaging.”

See Eat broccoli sprouts for your skin! and Eat broccoli sprouts for your hair! for similar studies.

Owl before sunrise