Is it fine to use skin whitening cream on penis or on testicles?

Diagnosis dependant!: Using lightening creams to the genitalia may be ok, but it depends on your underlying diagnosis. Hydroquinone's are typically the agents used to bleach out dark colors, but chemical peels and lasers are also being used along with new fading creams. I would exercise caution in bleaching the genitalia and visit an experienced urologist or dermatologist prior to treating.

Whitening cream: Most of those contain hydroqinone, which may irritate the skin so i would rec no.

Skin whitening cream: People who have areas of darker skin, often try to lighten the darker areas so all their skin is the same color. This can be done by using skin lightening creams, sometimes called skin bleaching creams. They almost always contain the chemical hydroquinone, and you can buy this cream with 2% without a prescription. They are safe, and rarely cause irritation. They take a long time to work.