Since fourth grade, I had bumps on arms, progressively got worse (now in high school)
I really don't think it's just keratosis pilaris because it's not itchy or rough (it looks rough in the picture only because
I recently tried 10% bp) and there's this white stuff that comes out when I pick on them, I believe it's sebum. There's just tons of bumps where no hair grows cause it's blocked and there's white stuff inside.{if it's red and swollen it's cause I picked at it}
Unfortunately, it's worse in real life than in the pictures
My main gripe is that literally every pore that is even slightly raised (and there's a lot of them) has a good amount of white stuff inside and just knowing that fact is depressing
Does Keratosis Pilaris have white soft substance inside the pores? (I thought it's sebum)
and how the hell do I get rid of it?
currently just on st Ives and gold bond because my arms are dehydrated due trying bp too strong. I've tried glycolic, amlactin, Paula's BHA but I have recently discovered that Head and shoulders might help. 
My son has the same thing and he was recently diagnosed with keratosis pillaris by his pediatrician. We were there on another matter and he noted that since he was 16 he was right in the height of puberty, noting the oily complexion, acne, facial and body hair, and also gave a name to his body blackheads (KP). I couldn't decide if it was KP or PF but the doc confirmed it. The KP has gotten progressively worse since age 13, and sometimes the bumps get inflamed and turn into full-blown acne. We've been treating his back and shoulders with the Acne.Org Body Regimen for his inflamed acne, plus some tretinoin .05% we got from the derm which we were using for his face for blackheads. We don't use the tretinoin every day, maybe a few times a week. It seems to be helping to smooth things out, as well as draw the hard, grainy sebum out so you can scrub it away with some soap and a washcloth. He also washes his hair a couple times a week with Nizoral antifungal shampoo and this also seems to be helping. Since we began this a few months ago his back and shoulders look better and things aren't getting out of hand anymore.
My advice would be to see a doc or a derm who can diagnose your condition and recommend treatment.
Hope this is helpful! 