These bumps are likely due to heat rash or folliculitis, both of which are triggered when sweat, bacteria, or yeast become trapped in the pores. This is common in hot and humid weather or after heavy sweating. Keep the skin cool, wear loose cotton clothing, and shower soon after sweating using a gentle cleanser. Avoid scratching, and use a light moisturiser if the skin feels dry or irritated. If the problem persists, worsens, or develops pus, please consult a doctor for proper diagnosis and treatment.