Never underestimate the power of the mind. Without reading it properly i can't comment on the methods listed in the given link but i have no doubt that the role that the state of our minds plays with our over all health is underplayed by the medical community.
Not sure how it affects our skin but remember that we have a gut brain axis so everything is interconnected.
Happiness and health are well correlated so i imagine skin would be too.
In general people who live the longest tend to be those who don't dwell on things etc.
Our past ancestors and those who still live in tribes etc had/have much simpler lives. No worrying about stupid things like "Do i have the right clothes/car/house/etc?" Things like bills, debts etc.
"Development" comes at a price.
The interesting thing is that the author deals with much more than just the relation stress-acne. The book advocates that even things that you have incorporated into your vision of yourself may be the cause of your skin problem. For example, something that deeply marked you in your infancy, or your behavior towards love, protection and sex.