Question: why do some pimples have hard pus?
Answer: Pimples with pus appear from both inflammation and as an immune response to the clogged substances in your pores. Pus only occurs in inflammatory acne. Noninflammatory acne (like blackheads and whiteheads) also involve clogged pores, but the resulting comedones are filled with hardened oil and dead skin cells, not pus.