There are a lot of myths floating around the internet about whether stress and acne are related in some way. I think it's evident that stress does cause acne, for the following reasons: When someone feels "stressed" their body attempts to compensate in a very ancient way. The adrenal glands, located above the kidneys, secrete certain types of hormones that help to resolve what used to be a "flight or fight" response.
Most of us don't have to focus on immediate danger very often but the body has not adapted to modern living. So you have hormones like norepinephrine, testosterone and cortisol pumped into your bloodstream whenever you feel stress. Testosterone, of course, is going to have a direct effect within the oil gland, causing more oil to be produced. That causes a chain reaction whereby you have the potential for inflammation going on underneath your skin. And when cortisol enters the picture, your ability to heal those pimples diminishes.
If the question to ask is "How do I reduce stress?" then the answer lies in understanding some of the ways you operate emotionally. For example, there are certain personality styles that are more prone to stress responses, such as the Mercurial and Dramatic styles. You can read about them in a book called "The New Personality Self Portrait". While these two seem to be the most outwardly demonstrable in terms of showing stress, any of the other 12 styles have their own way of expressing stress.
Stress is caused by your perception of the events in your life. If you believe that something is bad for you (and you are prone to drama) you will experience stress. The key is to identify and discard any beliefs that support a stressful response. One of the most effective ways to change thought patterns quickly is by reframing (an NLP concept). In its most simplistic terms, reframing is taking an event that you otherwise consider bad and figuring out how to make it good. For example, someone you wanted to go out with isn't interested in you. You really liked that person. Now you feel devastated, rejected. Instead of telling yourself things like "I'm not attractive/intelligent/smart enough", you tell yourself, "That's not bad, that's good. Now I don't have to put up with his crappy music."
Reframing takes practice so don't give up after the first attempt at it. Ultimately, you will find yourself feeling less stress as you apply the technique to all areas of your life. And once you've done that, you may find that your acne is occurring less often than usual. And that means your treatment regimen will work better.
Stress and acne are related. But if you work on the stress by eliminating your negative beliefs, you'll find that you enjoy life more, even while you search for the acne treatment that works best for you.