The New York Times reports:
The official line from the White House, as with other matters surrounding the president’s physical health and appearance, is that Mr. Trump’s glow is the result of “good genes,” according to a senior administration official who would speak only on the condition of anonymity.
Certainly Mr. Trump, who has long taken antibiotics to treat rosacea, a condition that can make the skin appear rosy and ruddy, is attentive to how he looks on television. He has complained that his skin and hair appear too yellow or orange on the screen, according to one person familiar with his views.
As a result, events in the White House are now more dimly lit than in previous administrations. The president has also become a fan of natural light, like the setting of the White House Rose Garden, where Mr. Trump chose to announce the end of the government shutdown in 40-degree weather.
At the link you’ll find a lengthy discussion on whether Glorious Leader uses a secret tanning bed or self-tanning lotions. Even White House insiders appear not to know.