When using new skincare products or a brand-new regimen, you should give it about three months, but expect to see some slight improvement after 3-4 weeks of usage. If you are still breaking out after three months or don't see any improvement in your skin after one month, switch to something else. Three months is enough time for your skin to renew and push the would-be pimples out of your clogged pores.
If you want to limit the severity of a purge, introduce the new product slowly to your skin, which can help. Start at a lower concentration or smaller amount, or use less frequently before gradually increasing to the recommended amount. Or you can always patch test.
So what do you do when your skin freaks out, and you don't know which product is causing the issue? Stop everything you're using: makeup, moisturizer, sunscreen, etc. Use mild topical hydrocortisone cream on your skin until your reaction decreases. Start adding products back in slowly. Eventually, you'll find out what's offending your skin. If your skin continues to react, see a dermatologist or skincare specialist, as it may be a more serious medical condition that needs special treatment.
Other than that, give your new skincare products a chance. Your skin may initially react to a new product with pimples and breakouts. After a while, your skin builds immunity to the products, and the breakouts subside.
Click here for more advice on starting a skincare regimen with active ingredients.