According to Sammy, his skin was damaged after years of playing in the sun and needed "rejuvenating", and the bleaching is just a side-effect of the cream, albeit not a side-effect he cares enough about to stop using the cream, which I call Creme de Sosa. When he does stop using Creme de Sosa for long enough, his skin does return to its original, dark pigmentation.
Now, granted, it's not that I don't believe him, but this is a man who had a camera on him every day for almost twenty years, and I never noticed anything wrong with his skin, although this was before HD cameras. Ignoring the obvious difference in color, his skin is a lot smoother now than it was in 2009 when he first started Creme de Sosa, so maybe something was up with his skin, but he's never said what.
There is a complicated history of racism, or more appropriately colorism, in the Dominican Republic, but I honestly don't think Sammy is a self-hating racist as Woke Twitter has accused him of being, otherwise he wouldn't have allowed himself to become black a couple times, and he still identifies as black. It would make more sense to say it's just classic Dominican Colorism, but if Sammy really does suffer from self-hate, he doesn't show it publicly.
I've spent more time assessing Sammy's life choices than anyone not named Sammy Sosa has any right to, but the best explanation I can come up with for what drives Sammy to occasionally turns himself white, is that he likes how he looks. There are some steroids which cause vitiligo-like symptoms as a side-effects, but Sammy didn't appear to start ahemALLEGEDLY juicing until his late 20s, and steroids don't usually do unexpected shit to your body unless you start when your body is still naturally growing, and there's no way to know whether or not the steroids he — allegedly — used were among the types of steroids that cause vitiligo-like symptoms unless he were to admit which alleged steroids he allegedly used, allegedly.