Development of an objective comedogenicity assay.

The rabbit ear comedogenicity assay is useful as a screening procedure for evaluating agents that come in contact with human skin. Controversy exists regarding the reliability of this assay because of differences in results from various laboratories. The subjective nature of the standard method of grading may also contribute to this variation. We use a more objective comedogenicity assay that utilizes increasing follicular orifice size on the rabbit ear as a measure of comedogenic activity. A generally linear increase in the degree of follicular orifice area was noted with several agents evaluated over a four-week application period. Further, a noninvasive Silastic elastomer mold was used to allow measurement of the same follicular orifice areas over time.

Variation in cutaneous perfusion due to synthetic pyrethroid exposure.

Synthetic pyrethroids are neurotoxic insecticides with a low mammalian toxicity. Prior investigations have found these agents to be neither cutaneous irritants nor sensitisers. Clinically demonstrable inflammation, as judged by erythema, oedema, or vesiculation, has not been apparent. Nevertheless, paraesthesia does result from cutaneous exposure. In this investigation technical grade flucythrinate was applied to the forearms of human participants twice daily for five consecutive days. Laser Doppler velocimeter measurements were made before each topical application, with histamine phosphate being intradermally injected on termination of the study. Results of both laser Doppler velocimetry and histamine induced axon reflex vasodilatation were not statistically significant at an alpha = 0.05 level. This investigation suggests that the synthetic pyrethroids have little influence on neurogenic vasodilatation on topical exposure.

Variation in cutaneous sensation between synthetic pyrethroid insecticides.

Synthetic pyrethroids are potent insecticides, utilized for food protection and general pest control. Numerous investigations have indicated that ultra-low volume applications are effective and may eliminate the developing problem of resistance to the currently utilized insecticides. The most prominent health symptom that accompanies topical contact with these agents appears to be a cutaneous sensation, paresthesia. In this investigation, a substantial difference in the degree of paresthesia was noted between the formulated grade of 4 synthetic pyrethroids. Also, dl-alpha tocopheryl acetate was statistically validated as an efficacious therapeutic agent for cutaneous exposure to these insecticides.

Synthetic pyrethroid insecticides: a dermatological evaluation.

Synthetic pyrethroids are lipophilic insecticides whose biological activity seems to be directly related to their chemical structure. In this investigation differences in cutaneous sensation were detected by human participants between synthetic pyrethroids with a cyano group in the (S)-configuration of the 3-phenoxybenzyl alcohol of their molecular structure (fenvalerate) and those that do not (permethrin). A strong relation was noted between insecticidal potency and degree of induced cutaneous sensation for the alpha-cyano and non-cyano pyrethroids, with a prominent difference between the two. No sensation was observed by any of the same participants on topical exposure to the inert ingredients of these agents. A linear correlation between concentration and degree of induced dysaethesia was observed for both pyrethroids. Regressing the cutaneous sensation on the common logarithm of concentration resulted in a regression equation of Y = 84.0 + 31.0X1 for fenvalerate and Y = 27.5 + 15.8X1 for permethrin. A highly efficacious therapeutic agent for pyrethroid exposure was noted to be dl-alpha tocopherol acetate. An impressive degree of inhibition of paraesthesia resulted from the topical application of vitamin E acetate, with a therapeutic index of almost 100%.

Topical zinc therapy for acne vulgaris.

A double-blind study of 30 patients with mild to moderate acne vulgaris was conducted to evaluate the efficacy of a topically applied 2% zinc sulfate solution for acne therapy. Over a 12-week period, no difference was noted between placebo- and zinc-treated participants in regard to either the number or type of acne lesions. The irritancy due to topically applied zinc was significantly greater (p less than or equal to 0.05) than that due to the placebo. Zinc serum levels were not significantly elevated between the two regimens before, during, or after treatment. This study suggests that topical zinc therapy alone is not of significant benefit in the treatment of acne vulgaris.

Primary irritant contact dermatitis from synthetic pyrethroid insecticide exposure.

Synthetic pyrethroids are widely used insecticides with numerous applications, varying from food protection to general pest control. Humans are capable of tolerating greater acute and chronic exposures to the pyrethroids than to many other insecticides. An abnormal cutaneous sensation (paresthesia) is known to occur after dermal contact with the pyrethroids. Recent field studies have indicated that a primary irritant contact dermatitis may also develop. This investigation evaluated dermal irritancy from cutaneous synthetic pyrethroid application to albino rabbits. Through repeated daily applications of either fenvalerate or permethrin, a slight erythema was noted visually which correlated with increased cutaneous blood flow measured by laser Doppler velocimetry. Histopathological changes were also documented, but no significant differences were detected in edema or thermal variation.

Inhibition of cutaneous paresthesia resulting from synthetic pyrethroid exposure.

Synthetic pyrethroids are potent lipophilic insecticides recognized as nerve toxins. Their increased usage in recent years has established them as a serious competitor against the currently available pesticides. Reported cases of occupational exposure have noted the presence of paresthesia without the clinical symptoms of erythema, edema, or vesiculation. Pilot studies were performed with six prophylactic agents to assess their capability of preventing or ameliorating the paresthesia that accompanies exposure. Vitamin E oil (dl-alpha tocopheryl acetate) proved the most efficacious.

Paresthesia from cutaneous exposure to a synthetic pyrethroid insecticide.

Occupational exposure to fenvalerate, a synthetic pyrethroid insecticide, has been reported to cause paresthesia. An assay was devised in our laboratory for subjective grading of the sensation produced by the topical application of this compound. The present double-blind study compared human discrimination of topically applied technical fenvalerate, the heavy-ends fraction of fenvalerate, and ethyl alcohol (vehicle). Both forms of fenvalerate showed a statistically significant increase in inducing paresthesia over the vehicle alone. The onset of the cutaneous sensations occurred at one hour, peaked at three to six hours, and lasted approximately 24 hours. Numbness, itching, burning, tingling, and warmth were the most frequently reported sensations. The difference between the two fractions of fenvalerate was not statistically significant.

Comparison of topical clindamycin phosphate, benzoyl peroxide, and a combination of the two for the treatment of acne vulgaris.

Patients with moderate to severe acne vulgaris were treated for 10 weeks with either topical clindamycin phosphate (1% solution) twice daily, benzoyl peroxide (5% gel) twice daily, or benzoyl peroxide (5% gel) in the morning and clindamycin phosphate (1% solution) in the evening. The effects of each regimen appeared to vary in decreasing specific types of acne lesions, with the combination therapy showing the greatest decrease when all types of lesions were considered. Cutaneous side-effects were greatest with benzoyl peroxide alone during the early weeks of treatment, while the combination therapy displayed no greater incidence of redness, scaling, or itching than clindamycin phosphate alone. All three regimens produced clinical improvements which did not differ significantly from each other.

Scapular reactivity to contact irritants: application-time and area variations.

Twenty-two diurnally active, fair-skinned, male volunteers were repeatedly patch tested with 10, 15 and 20% lapyrium chloride (LC) and 0.3 and 0.5% sodium lauryl sulfate (SLS) for 5 consecutive days. A series of 5 patches containing SLS and LC were placed vertically once daily for 6 h on different sites of the scapula: paravertebral, lateral and medial. The sites of application were randomized over subjects for patch testing once a day per area at either 08%, 16% or 00%. Each patch was left in place 6 h; scoring of each site, using a 13-point scale, was done 2, 10 and 18 h after removal. The cutaneous reactivity varied in a statistically significant manner according to the time and area of patch application. For each day except the first, LC scores exhibited highest and lowest responses at 16% and 00%, respectively. For SLS, a statistically significant application-time difference in reactivity was detected only for the readings of day 2 when scores were highest at 00% and lowest at 16%. Intraregional variations in scapular reactivity were also exhibited. Strongest reactions to LC occurred in the center of each scapula; weakest reactions were elicited on either the lateral or paravertebral sites. For SLS, statistically significant intraregional differences in reactivity were detected only for the second day of patching, with strongest responses near the spinal column and weakest near the axilla.

Cutaneous effects from occupational exposure to fenvalerate.

The purpose of this study was to determine, through a field survey, the prevalence of cutaneous response to the synthetic pyrethroid fenvalerate; to characterize the cutaneous reaction; and to identify the setting in which it occurs. The methodology involved case studies of selected individuals who had worked extensively with fenvalerate in the delta region of Mississippi and Alabama. All the agricultural workers interviewed and examined had, on some occasion, noted a paresthesia which they associated with exposure to this pyrethroid insecticide. The cutaneous sensation described was a stinging or burning which progressed to numbness in approximately one-third of the exposed workers. The sensation typically began a number of hours after contact, peaked in the evening, and rarely was present the following morning. The intensity of the sensation varied according to the type and extent of exposure. Clinical signs of inflammation such as edema or vesiculation were not apparent. Erythema was present in a limited number of individuals but was not distinguishable from sunburn. Several environmental factors were found to affect the cutaneous sensation associated with fenvalerate exposure.