It is widely suspected that the anaerobic bacterial species Propionibacterium acnes ( P. acnes ) contributes to the development of acne, but its exact role is not well understood.  There are specific sub-strains of P. acnes associated with normal skin, and moderate or severe inflammatory acne.  It is unclear whether these undesirable strains evolve on-site or are acquired, or possibly both depending on the person. These strains have the capability of changing, perpetuating, or adapting to the abnormal cycle of inflammation, oil production, and inadequate sloughing of dead skin cells from acne pores. Infection with the parasitic mite Demodex is associated with the development of acne.   It is unclear whether eradication of the mite improves acne. 
The best hydrocortisone cream is only available by prescription, so you will have to see a dermatologist if you want to use this cream. You can use a less powerful over the counter hydrocortisone cream for acne if you prefer. You might not see the desired results as fast as with a prescription based topical cream though, but you won’t have to see a doctor. A product that has received some good online customer reviews is Aveeno and Cortaid Maximum Strength , which contains 1 % hydrocortisone, which is the maximum amount that can be used without a prescription.