TL;DR Summary: This got quite long, primarily because it was very interesting to follow around various sources and try to cross-check them. My summary:
- The claim that fluorinated toothpaste causes acne around the mouth is definitely widespread
- There was at least some indication via an un-controlled experiment by a dermatologist in 1975 that indicated that, assuming other variables remained unchanged, cessation of fluorinated toothpastes among ~60 patients caused a significant reduction in acne
- There appears to have been no replication of this experiment under more stringent conditions to test the hypothesis and thus it remains unconfirmed
- There are sources linking other fluoride-containing compounds, namely steroids, to perioral dermatitis, a form of acne.
- In my digging (which you'll see below was reasonably extensive), all claims for this connection either 1) contained no sources or 2) tracked back to this 1975 dermatologist's editorial letter
My digging seems to come up with this as an unresolved question that will require a further study. The link you posted may feature the original source for this claim, namely THIS, a letter to the editor of the Journal, Dermatology, by Dr. Milton A. Saunders in 1975 entitled "Fluoride Toothpaste: A Cause of Acne-like Eruptions," summarized here:
- Saunders was treating ~60 patients between 20-40 years of age with acne around chin area that were resistant to treatment and swore that such acne was not from hand/mouth area contact or wearing cosmetics
- Saunders wondered what else might be the cause and thought of fluoride-containing toothpaste
- He asked the patients to switch to non-fluoride-containing toothpaste and 50% cleared up; the remaining 50% remained as they were, with acne
- The asked the patients still afflicted to switch to baking soda and Scope mouthwash, and almost all of these patients cleared of almost all of their acne
- Some patients who had achieved an improved state switched back to fluoride toothpaste and their acne returned
Fairly impressive so far. In continued hunting, I found a response HERE from Dr. Ervine Epstein to Dr. Saunders which appeared in the same journal a year later (1976). It stated:
I read the letter from Dr Saunders on fluoride toothpastes as a cause of acne-like eruptions. His observations are interesting and possibly important. However, I would like to offer the following comments: (1) The ingestion of fluorides neither precipitates nor aggravates acne. (2) Fluorides are much more closely related chemically to chlorides than to iodides or bromides, although all are halogens. There is no evidence that chlorides per se cause or irritate acne. (3) Dr Saunders has not established that nonfluoride toothpastes do not cause acneiform eruptions. (4) A survey among dentists indicates that, due to the efforts of Madison Avenue, 60% to 80% of all people, and especially women, use fluoride toothpastes. Therefore, 46 out of 46 cases is less impressive. (5) It has not been established that the fluorides in the toothpaste are the actual cause of the eruption described by Dr Saunders.
Dr. Saunders published a response that same year in Dermatology, stating:
First of all, the letter to the editor was not intended in any way to represent a well-controlled scientific study of statistical significance; rather, it was an observation that I hope will encourage others to investigate the subject more thoroughly in a double-blind, large-scale study, so that it may be established whether these observations are valid. In reply to the numbered comments in Dr Epstein's letter, I submit the following: Dr Epstein stated that the ingestion of fluorides neither precipitates nor aggravates acne. No implication that the ingestion of the fluorides had anything to do with the acne-like eruptions involved was made or intended in my letter. Rather, I suggested the possibility that salivary nocturnal drainage may carry fluorides...
Now, all three of these are inaccessible to me, so I'm not sure what the full text might reveal.
There's an article from Pediatrics and Child Health found HERE entitled "Treatment of acne vulgaris" in which the following is found under the heading, perioral dermatitis (emphasis mine):
Papules, pustules and erythema in the perioral, paranasal or periorbital areas, sparing the lip border, characterize perioral dermatitis. Possible triggers include potent topical steroids, chemicals (cosmetics, toothpaste), local infection, hormonal changes, sunlight and rarely foods.
Since further digging around the areas of "acne" and "fluoride" and "toothpaste" were not bringing up anything new, I thought I'd focus on this particular condition since it's at least a more specific term to examine.
I found conflicting "layman" evaluations of whether perioral dermatitis was acne or not. Some state that it is an imposter or a rash, however THIS 2008 article from the Open Journal of Dermatology states:
Perioral dermatitis is a facial condition that looks often like a rash, but is a form of acne.
So with that out of the way, here's some sources on perioral dermatitis:
- A blog-like site dedicated entirely to this condition, perioraldermatitis.net states:
Recent studies prove on one side that fluoride toothpaste can cause perioral dermatitis**, or if the condition already exists, it can be aggravated. In recent studies, it is shown that most of the patients suffering of this condition stopped using toothpaste containing fluoride and switched to another type of toothpaste, approximately half of their lesions disappeared within four weeks. Patients who started using again dermatitis toothpaste with fluoride, developed a recurrence of the disease.
This sounds suspiciously like the Saunders experiment above (references to half of their lesions disappearing (though Saunders reported that half of the patients had a decrease in acne) and the re-occurrence of symptoms when switching back to fluouride-containing toothpaste). If so... 1975 isn't a year I would put under the category "recent" in terms of medical understanding. No source is given for the claim...
- WebMD states the following about perioral dermatitis:
The exact cause of perioral dermatitis is not known. However, it may appear after topical steroid creams are applied to the face to treat other conditions.
One might expect toothpaste to make this list if it were a well-known, study-proven cause.
- THIS article from the American Osteopathic College of Dermatology states the following:
There may be more than one cause of perioral dermatitis... Overuse of heavy face creams and moisturizers are another common cause. Other causes include skin irritations, fluorinated toothpastes, and rosacea.
Same fluorinated toothpaste comment; no source is provided.
Wiki lists fluorinated toothpastes as a cause of perioral dermatitis as well, citing no source. However, following the link for glucorticoids reveals a journal article from The Annals of Allergy, Asthma, and Immunology entitled, "Disease management of atopic dermatitis: a practice parameter (LINK), which contains the following under the "Management" section (as in, how to manage dermatitis):
Potent fluorinated corticosteroids should be avoided on the face, the genitalia, and the intertriginous areas as well as in young infants
So, there may be something to be said for fluorinated compounds, at least steroids, being avoided on the face due to a potential risk of dermatitis. Nothing about fluorinated toothpaste.
To close, the waters appear murky, very possibly due to an old source that has never been experimentally verified under controlled conditions, and thus in the absence of known causal factors with respect to perioral dermatitis (and many sources state that the exact cause is unknown and do not list toothpaste), these old sources and folk theories have been substituted for the simpler phrase, "We don't know."
The fact that fluoride-containing steroids are also known to cause or agitate this condition may not help the situation, and perhaps the various regurgitators of information use this to boost the possibility that fluoride-containing toothpastes might also be a cause.
I'd end by saying that in Saunders' 1976 reply to Epstein, he states that his theory is that fluoride-containing saliva is the cause of acne. Thus, if one could eliminate drooling or coating of the mouth area with saliva after brushing teeth, or determine the mechanism of fluorinated compounds causing acne and verify that the levels in saliva post teeth-brushing are not high enough, we might also be able to test the theory via those routes.
By far, the best thing that could ever happen to this question is to have a controlled experiment of large sample size done to test it. My counts-as-nothing hunch is that if such a thing hasn't been done in almost 40 years... there at least hasn't been enough interest in the possibility to drive such an experiment, increasing my probability estimate for the myth being unfounded.