That is someone's neck tilted -90 degrees.

I have those too, on my face! Hehe, I don't know whether it is just papules or nodular acne but either way it is inflammatory so; a) don't scratch, touch or rub them, it may burst and/or most likely spread. B) be patient, they will take a WHILE to go away. C) if a is not followed strictly, they will SCAR!!

Now as to what is causing them, look no further than what goes around your neck; hair = greasy hair products, sweaters, shirts, scarf, jewelry etc and try to find the culprit that you can live with eliminating.

Even with benzoyl peroxide, they don't magically fade away, slow burn, gotta weather the storm.