After being plagued with acne for years, I took a job which caused me to work in remote bush camps for short periods in the far north. My acne would invariably disappear within a few days of exposure to this. When I returned to the city, the acne would return with a vengeance. Did not know why.
My theory: Soap residue left after washing my face with hardwater was the true acne culprit. Washing my face with ultrasoft lake water in bush camps leaves little or no soap residue, so no acne. Soap residue stimulates excessive skin oil secretions which leads to increased acne. A rich diet aggravates the problem by feeding the oil secretions.
My self-experiment: I experimented with different types of soap and different concentrations of soap in hard and soft water.
Conclusion: Soft and slightly soapy water only (a very mild soap) produced the least amount of acne. Never apply soap lather directly to your face! If you have only hard water to work with, then no soap at all is the best choice by far. Compensate for the lack of soap with hotter water.
Added benefit: Washing your face with no soap causes acne lesions to heal much faster – a couple of days compared to a week or more with soap.
The same technique applied to cold sores.