After topical antibiotics and/or retinoid and/or benzoyl peroxide, dermatologists commonly prescribe oral antibiotics, but why?
Presume that the patient dutifully consumes the full prescribed course of antibiotics.
Antibiotics may reduce the number of, but can't kill to the last drop Cutibacterium acnes.
Normally acne sufferers don't live in a sterile environment, and C. acnes may be floating in the air or lying on surfaces. Even if antibiotics kill every single bacterium of C. acnes this time, it'll probably colonize you again and regrow. C. acnes is
largely commensal and part of the skin flora present on most healthy adult humans' skin. It is usually just barely detectable on the skin of healthy preadolescents. It lives, among other things, primarily on fatty acids in sebum secreted by sebaceous glands in the follicles. It may also be found throughout the gastrointestinal tract.
Oral antibiotics mustn't be consumed forever.
After antibiotics kill most of the C. acnes and the patient stops taking the antibiotic, the remaining C. acnes (perhaps now resistant to that antibiotic) will proliferate to its formerly high concentration, and cause acne again.
My argument befits the comments beneath.
I took 50mg/daily for about two years and it worked a treat but when I stopped taking it the acne came straight back.
It's just once you've stopped taking the antibiotics, there's going to be a period of several weeks/going into months where your skin might be getting worse because you came off of the anitbiotics - or might be because of reactions to the new topicals.