No. No amount of masturbation ("excessive" or otherwise) causes acne.
Self-help forum and product retailer, Acne.org explain on their Acne Myth page:
This antiquated notion, originating as early as the 17th century to dissuade young people from having premarital sex, is not based on scientific evidence.
Masturbation and Acne
Is there a correlation between acne and masturbation? I do not answer this in this answer, but I do argue any correlation is weak, and I look at other ways acne and masturbation might be correlated, and yet still not be causally related.
For this discussion, "acne" is regarded as a full-blown severe case covering substantial areas of skin, and not the occasional lonely zit.
Correlation, if any, is weak
The number of people with acne is much lower than the number of people who masturbate.
From the Planned Parenthood Federation of America:
Masturbation is very common. Studies show that about 7 out of 10 adult men and more than 5 out of 10 adult women masturbate. It’s also common for children and teens to masturbate.
From Acne.org:
Adult acne affects 25% of all adult men and 50% of adult women at some time in their adult lives
So, looking at the male population, 70% of male masturbate only 25% have acne. (The numbers for women are closer.)
If there is a correlation between masturbation and correlation it can't be a strong one. Masturbation doesn't automatically lead to acne.
Hormones
Hormones may cause acne.
Acne.org argues on their Acne Myth page that any correlation may be caused by androgens:
A more plausible explanation may be that higher levels of androgens (male sex hormones) can cause increased sex drive. We also know that high levels of androgens can be related to more severe cases of acne. So it may be the higher androgen levels and not the associated increase in desire for sexual activity that is related to acne.
Testosterone is an androgren that is related to acne and sex-drive and hence might be related to masturbation.
The relation of testosterone and acne:
Most dermatologists believe acne is closely linked with hormonal changes that occur within the body. In fact, testosterone has been identified as a chief trigger of acne development. According to the American Academy of Dermatology, testosterone works to stimulate oil gland activity, creating an oilier skin more prone to acne breakouts.
Sources for this have also been:
Masturbation and Other Effects
A separate concept is what constitutes "excessive" masturbation. From Planned Parenthood Federation of America's Myth and Facts about Masturbation page largely dismissed the idea:
The myth is that too much masturbation will make you blind, crazy, or stupid, damage your sex organs, or stunt your growth. Some people masturbate every day — or even more than once a day. That's fine. So is there such a thing as "too much" masturbation? According to the experts (the American Psychiatric Association), it's only when masturbation gets in the way of daily activities — like going to school or work, or meeting friends — that it would be considered "too much." And not many people have that problem.
Also, some people worry that masturbating frequently will affect a girl's ability to get pregnant or a guy's ability to produce sperm. It doesn't.
Some people masturbate daily or more than once a day, some people masturbate once in a while, and some people never masturbate
However, I think that it's worth noting that they may be some negative side-effects to masturbation:
If a couple is trying to get pregnant the man should hold off from masturbation on the days before the woman's ovulation and only have sex (once a day or every other day) as it reduces the sperm count and will reduce the chance of successful fertilization, see here and here.
You can read more about the negative effects of masturbation here
