If the bumps are small, uniform, and itchy — and especially if they flared after sweating or a course of antibiotics — it may be Malassezia (pityrosporum) folliculitis, an overgrowth of a yeast that normally lives on skin. It's routinely mistaken for acne and won't respond to benzoyl peroxide or retinoids; antifungals tend to clear it quickly. A review in the Journal of Clinical and Aesthetic Dermatology describes exactly this pattern and misdiagnosis (https://pubmed.ncbi.nlm.nih.gov/24688625/).
The tell vs. real acne: acne is usually a mix of sizes and types (blackheads, whiteheads, cysts); fungal folliculitis is monotonous and itchy. This is a genuinely "see a professional to confirm" situation, because the correct diagnosis changes the whole plan. Malassezia also feeds on certain oils/esters, which is the basis of the "fungal-acne-safe" ingredient idea — that ingredient-avoidance evidence is weaker than the diagnosis itself, so treat it as a helpful heuristic, not a cure.