Here is some background information on "Dumb" from songfacts.com :
A drug-themed song, this relies on the theory that "Ignorance is bliss." Kurt Cobain compares repairing a broken heart with inhaling "glue."
The lyrics, "Skin the sun, fall asleep, wish away, the soul is cheap, lesson learned, wish me luck, soothe the burn, wake me up" equate to how it feels so good to fall asleep in the sun, never mind the consequences of sunburn as in the consequences of a passionate relationship or drug use.
The most noticeable drug reference is, "My heart is broke, but i have some glue. Help me inhale, and mend it with you," meaning getting over a heartbreak with the high from glue and maybe finding a drug buddy with it.
Along with some other In Utero songs, many fans heard bootleg versions of this long before the album came out. At the Reading Festival in August 1992, this became clear when the audience started singing along.
