How well does hydroquinone work to fade scars?

Fairly well: Hydroquinone is an effect way to fade hyperpigmented scars (those with a dark color) but it is not as effective at fading red or raised scars. Those require other measures. Also in a small number of dark-skinned individuals, use of hydroquinone can cause increased pigmentation. Nothing works 100% of the time so for best results, consult with an expert in scars e.g. A plastic surgeon.