The first author to describe a red-orange fluorescence in acne patients was Bommer 1 using ultraviolet light. The fluorescence has been attributed to the presence of porphyrins produced by Propionibacterium acnes. These substances, when illuminated with ultraviolet rays of wavelengths between 320 and 340 nm, emit a red-orange fluorescence 2. A recent study showed that the detection of this fluorescence is useful to distinguish the follicles populated by bacteria from the ones that are not 3. McGinley et al. 4 affirm that the presence of a colony of at least 1000 P. acnes in the follicle is required for the red fluorescence to be noticed.
There are several plausible explanations for the decrease in fluorescence after treatment: the killing of P. acnes, suppression of the production of porphyrins, destruction of porphyrins, and reduction in sebum secretion. Most probably, these mechanisms act synergistically, leading to a reduction in porphyrins 5. Other studies have shown that the intensity of fluorescence is correlated to the density of P. acnes on the skin surface and directly related with its reduction observed after treatment 6–11.
Fluorescence was used in the past to evaluate the effect of different therapeutic aids. Lucchina et al. 12 showed that after treatment with clindamycin (1%) for 12 weeks fluorescence significantly decreased on comparison with controls. Three years later, another study evaluated the suppression exerted by benzoyl peroxide (BPO) on P. acnes 6. In their study, the decrease in fluorescence corresponded perfectly to the logarithmic decrement in the count of P. acnes. More recent studies questioned this assumption, observing that the orange fluorescence is strongly correlated with the presence of sebum and not only with the presence of P. acnes 13,14.
Youn et al. 14 concluded that the red fluorescence cannot be attributed solely to P. acnes but it is probably related to the secretion of sebum, as samples taken from areas where red-orange fluorescence was detected were negative for P. acnes. A significant correlation was found between the skin surface pH and red fluorescence: the fluorescence was more evident in areas where pH is increased. This observation probably implies that fluorescence is affected by other substances that could be changed by pH of the skin.
Dobrev 5 found a significant positive correlation between the red-orange fluorescence and the casual sebum level. According to the findings of Youn et al. 14, the sebum amount and area of fluorescence spots were not correlated to the clinical grade of acne.
Choi et al. 15, in a study on 878 patients, supported the hypothesis that the origin of facial red fluorescence is correlated to sebum composition. In patients with acne, the intensity of fluorescence in the U-zone showed a positive correlation with the casual sebum level and the number of acne lesions. In the T-zone, the fluorescence intensity was correlated with the casual sebum level but not with the number of acne lesions.
We present a few observations made by us during our clinical practice. We analyzed the fluorescence patterns in acne patients using the Dino-Lite digital video microscope AM413T-FVW (Italeco Srl, Turin, Italy). It allows skin observation under polarized parallel light and ultraviolet light. The illumination is produced by four ultraviolet light-emitting diodes (emission filter cutoff wavelength: 425 nm) or, alternatively, by four white light-emitting diodes. The instrument has a resolution of 1.3 megapixels and a variable magnification of ×10 to ×92.
We analyzed three spots on the frontal region, three on each cheek, three on the nose, and one on the chin of the following patients:
- Five teenagers (mean age 16) with moderate acne were assessed. They did not use any topical or systemic drugs for at least 4 weeks before the beginning of the study. Thereafter, they underwent a treatment with BPO for 1 week. The changes in fluorescence induced by BPO were recorded every 2 days for a week.
- Five teenagers with severe acne were assessed before and after a month of therapy with oral isotretinoin.
- Five healthy volunteers of the same age were assessed.
- Five healthy adults between the ages of 50 and 70 years were also assessed.
We found different patterns of distribution of red fluorescence among our patients (Fig. 1). In healthy adults and adolescents, a red fluorescence was observed along the border of the ostium of the sebaceous follicles. It was more or less abundant from outside to inside: some follicles were totally red, whereas in the center of other follicles the fluorescence was bright white. The same profile was observed among adolescents with acne; however, they had a more pronounced red fluorescence (Fig. 2). Interestingly, in patients not previously treated topically or systemically, there was evidence of a red fluorescence in some areas of the skin that did not correspond to any visible lesion and almost completely disappeared after a short period of treatment with BPO. The red fluorescence did not seem to have a predictable and linear regression during therapy, as its variation was very different from one patient to another (Fig. 3). If this type of fluorescence is related to the sebum amount, it would take more time to disappear than a few days. We also observed fluorescence in patients treated with isotretinoin at a dose of 10 mg a day orally for 1 month. We had great expectations about the change of fluorescence after treatment; however, even after 1 month of therapy the fluorescence remained unchanged. These observations are worthy of further research. The analysis of the pattern of fluorescence could be useful during clinical practice for choosing efficient treatment modalities.
Conflicts of interest
There are no conflicts of interest.
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