These ghastly marks... almost lesions... are testament to the ergonomic monstrosity that is the DS Lite when grasped by the world's large-palmed super He-Men. What's causing this gruesome gamer stigmata? According to Pocket Gamer:

The problem - unsurprisingly - is the smaller size of the DS Lite, which means instead of being able to support your DS without it digging into your hand, you're more likely to end up grinding the more tightly curved bottom corner of the DS Lite into your palm where your life and head lines meet, as you frantically try to press the shoulder button and action buttons simultaneously... Another contributing factor are the flat sides of the DS Lite. The DS Fat, in contrast, has concave edges which spreads the contact over a wider area of your hand. The DS Lite's top edge does the opposite.

Of course, some of these issues could be mitigated by not grasping your DS Lite in a vice-like death grip. I — graced with soft, dove-like hands well attuned to the poet's life which I lead — don't have any problems with my DS Lite, but my hands aren't large enough to grasp a bowling ball like a skee ball, either. Florian Eckhardt

Why I've Gone Back To DS Fat [Pocket Gamer]