I have been getting pimple-like bumps on my arm. They do not itch or hurt most of the time. The end up popping like pimples, scabbing and scarring. ?

Folliculitis. The condition is possibly inflammation of hair follicles which can result in bumps, crusting etc. Rarely some areas may progress to micro abscess formation. Topical Bactroban (mupirocin) Cream offers relief and helps with the healing process.
Maybe KP? This sounds like a condition called keratosis pilaris. It is essentially due to trapped hair follicles with small ingrown hairs although the exact cause is not truly known. A wide variety of options ranging from chemical to mechanical exfoliation, urea treatments, retinoids and even laser hair removal have been used to mention a few interventions. Avoid picking/popping which leads to hyperpigmenta.

Related Questions

I have a pimple like rash (not red skin just bumps) under both upper arms, only itches when tshirt brushes up against it and doesn't hurt?

See your doctor. If you've recently changed your underarm deodorant, detergent washing clothes, or have sensitivity to this in your underarms, or upper arms, you need to have your doctor see it, and diagnose it properly, and treat it. It may be something very simple to do. Plus, you want it documented in your chart, or have photos taken. Good thing it doesn't hurt. Read more...
Pimple like . Rash - sounds benign . Just observe for now. Do take a picture for documentation . In meantime , cover it with a bandaid to avoid getting irritated by your clothing. Read more...