It varies from person to person. Not everyone breaks out at the same rate. For some people irritation break outs can show up by the next day and for others it may take several days. Some people experience an "initial breakout" several days to a few weeks after beginning a new acne treatment plan, and this sort of breakout does not necessarily mean that the product isn't working. In fact, this sort of breakout is telling you it IS working. Acne bacteria can sit latent under our skin for weeks before coming to the surface in the form of breakouts, and that "initial breakout" is just the body purging itself before the healing/clearing process can begin.

Also, and especially with over-the-counter acne products, there may be an ingredient that breaks out one person, but not another. This also varies from person to person. It's important when selecting over-the-counter products to look for "noncomedogenic," "oil-free," "hypoallergenic," etc. in order to avoid buying products that will clog pores and break you out. Neutrogena, CeraVe, and Cetaphil are all trusted brands and used successfully on here by many.

Keeping it basic and not using too many new products or treatments to once will help minimize irritation breakouts. Skin does best with only one treatment at a time, whether BP, salicylic acid, etc. For BP, using a 2.5% formula works best to avoid irritation breakouts. 5% and 10% BP formulas are way too harsh and don't clear acne any better. If anything, they contribute to irritation breakouts. And don't use BP and salicylic acid at the same time...pick one or the other or you may irritate your skin too much which can break you out.

Regardless of which topical treatment you choose, always be super gentle. Use a feather-light touch when washing your face and applying your acne treatment, don't rub or scrub your face, pat dry after showers, avoid touching your face in general. All these can help prevent irritation breakouts.

Hope this was helpful!

Thank you very much @DeLovely, it's very helpful..

i still have some follow up questions:

how can we know whether our breakout is due to purging/ due to our skin not compatible with the product or bad diet? and how long does the purging last usually? i have been using sodium hyaluronate as a serum for over a week (combined with salicylic acid cleanser), but it seems clogging my pores and I still have some whiteheads/pastules, so I'm not sure if it's because I'm allergic to sodium hyaluronate or purging effect... but purging usually happens for treatment products right not for serum/ moisturizer?

also do you know if dryness can trigger breakout? and can you recommend any non comedogenic moisturizer for oily skin people?

thank you again ! sorry if i asked too many questions...

Again it varies, and it can be tricky to tell the difference. You need to learn to be your own best skin expert and to read your skin. The classic "initial breakout" often happens anywhere from 3-6 weeks into a brand-new acne treatment. Oftentimes, your skin will clear up considerably, followed by a breakout. This purging process of clearing followed by breakouts can actually go on for weeks, but you'll start to notice that the breakouts are less and less and heal faster and faster, don't hang around as long as before. Over time, you'll see longer and longer periods of clear skin, with only like a few new pustules, or maybe one or two decent-size zits every so often, at which point you'll know acne is now under control.

Food-related breakouts are tricky. It's a huge game of trial and error to figure out which foods if any are breaking you out. I'd try eliminating one food at a time and see if you notice any impact. If after eliminating dairy for a period of say one month you notice your skin is much clearer, then chances are dairy was a contributor. Of course, if you're also doing a topicals regimen at the same time, then it will be hard to tell if it's the eliminating dairy or the treatment that's clearing you. But many on here have seen an improvement after eliminating dairy. And common sense will tell you that lots of sugary foods and grease are bad for you, so regardless of skin issues, always a good idea to eat a healthy diet when possible and drink plenty of water.

For oily skin, my favorite moisturizer hands down is the Acne.Org moisturizer. I no longer have problematic acne but I still swear by this for my oily skin. It's very hydrating and dries with a matte finish, so perfect for oily people like us! I also take hemp seed oil supplements every day and this has helped with oil control too. Other good moisturizers for any skin type are Neutrogena Oil-Free moisturizer and Olay Complete All-Day moisturizer.