Volume 11 Number 2, Part 1 August, 1984

Correspondence 309

search into the formulation basis of acne products so that some scientific proof is available to justify the use of comedogenic products on acne-prone skin.

James E. Fulton, Jr., M.D., Ph.D. 1587 Monrovia Ave.

Newport Beach, CA 92663

Fig. 1. Comedogenic effect on rabbit ears by Benzac W 1° and Desquam-X.

studies in California, comparing the effect of one commercial benzoyl peroxide product versus another. It has never been shown that Desquam-X is superior in its effect to a preparation such as Benzac W 1°, but you can see the marked difference in the irritancy and com- edogenicity from the photograph. We not only examine the outer ear but also look at the results deep in the ear canal. The reason that we use the outer ear is that it is much easier to photograph for your reader's visualiza- tion than the area deep down inside the ear. Please note that we compare the results in the rabbit ear against a negative control. We use the alternate ear for compari- son where nothing has been applied. By using this, I believe, you get a better rating scale than Dr. Klig- man's model, which compares the results in the treated ear to a positive control such as coal tar. So the two tests approach the same compound from the opposite position.

As far as the concentration of laureth 4 in cosmetics and therapeutic products, the concentration of 10% that we tested is not much different than the 6% used in an average formulation of ache preparations. I do not feel that this slight difference in percentage is "substan- tially a lower amount." Finally, it is becoming stan- dard knowledge in the industry that isopropyl myristate is graded on the rabbit "4 to 5" and not "1 to 2 ." This discrepancy has been reported from other laboratories, but independent investigators feel that it is a "4 to 5" grade too. At least one laboratory uses isopropyl myris- tate as a positive control instead of coal tar.

I think a picture is worth a thousand words, and I would like the readers of the JOURNAL to make up their own thoughts on the basis of the photograph that Desquarn-X does contain something that Benzac 1° does not. I hope that this controversy stimulates more re-

Chemica l composition for sa l tpe te r

To the Editor: In the article entitled "The Perforating Disorders"

by James W. Patterson (J A~ ACAD DERMATOL 10:561-581, 1984), on page 563 the following state- ment is printed:

Exposure of individuals to saltpeter (calcium chloride) has produced dermal changes indistinguish- able from those of PXE . . . .

I bring to the attention of the editorial staff and the author that saltpeter is potassium nitrate, rather than calcium chloride.

Joel E. Holloway, M.D. 900 N. Porter, Suite 1700, Norman, OK 73071

Reply

To the Editor: I thank Dr. Holloway for pointing out the error on

page 563 of my article entitled "The Perforating Disor- ders." As he has indicated, saltpeter is not calcium chloride. However, the particular form of saltpeter to which my reference pertained was not potassium nitrate.

Although perhaps the most familiar type of saltpeter is potassium nitrate, there are other nitrate compounds which have also been designated "saltpeter." These include sodium nitrate, sometimes termed "Chile salt- peter," and calcium nitrate, otherwise known as "Norway saltpeter. ''1 The Scandanavian article I quoted 2 and its companion piece 3 described a group of elderly men who years earlier had spread a fertilizer composed of "Norwegian hydrous saltpeter." The chemical composition of this material is as follows:

Ca(NQ)2 • 2H20, Ca(NOz)2 5Ca(NOs)2 • NH4NOa " 10H~O (the double salt) with 78% Ca(NO3)2, 6% NH4NOa, and 15% H~O

Affected individuals developed a burning sensation shortly after use, followed by cutaneous ulcerations in exposed sites. Ulcers healed in 2 to 3 weeks, leaving yellow-white papules and plaques. This condition was