Identification of factors associated with minimal erythema dose variations in a large-scale population study of 22 146 subjects

Patients With Rosacea Exhibit Lower Minimal Erythema Doses to Both UVA and UVB

BACKGROUND

Rosacea, a prevalent chronic inflammatory skin condition primarily affecting the central facial convexities, is categorized into four clinical subtypes: erythematotelangiectatic rosacea (ETR), papulopustular rosacea (PPR), phymatous rosacea (PhR), ocular rosacea (OR). While ultraviolet (UV) radiation is recognized as a risk factor for rosacea, the differential skin sensitivity to UVA and/or UVB between healthy individuals and rosacea patients remains ambiguous.

METHODS

This study comprised 70 patients diagnosed with rosacea and 100 healthy controls. The minimal erythema doses (MED-UVA and MED-UVB) were ascertained using an SUV-2000 solar UV simulator. A comparative analysis was conducted on the MED-UVA and MED-UVB results between the rosacea patient group and the healthy control group, as well as among rosacea patients with varying clinical subtypes. Furthermore, the correlation between MED values in rosacea patients and factors such as age, skin type, antinuclear antibodies (ANA), and the Clinical Erythema Assessment (CEA) scale was evaluated.

RESULTS

In comparison to the healthy control group, the rosacea group demonstrated significantly lower MED-UVA (p < 0.05) and MED-UVB (p ≤ 0.001) values. However, no significant differences were observed in the MED-UVA (p > 0.05) and MED-UVB (p > 0.05) values among patients with varying clinical subtypes of rosacea, specifically between ETR and PPR.

CONCLUSION

Patients diagnosed with rosacea demonstrate a decreased minimal erythema dose to both UVA and UVB, suggesting heightened sensitivity to ultraviolet radiation. Consequently, it is advisable for individuals with rosacea to minimize sun exposure in order to mitigate or prevent exacerbation of the condition.

Comparison of Minimal Erythema Dose Between Affected and Unaffected Skin in Vitiligo Patients With Fitzpatrick Skin Phototypes III, IV, and V

INTRODUCTION

Vitiligo is a depigmenting autoimmune disease. This study aimed to determine the minimal erythema dose (MED) of vitiligo-affected skin and normal skin among patients with skin phototype III, IV, and V.

METHODS

A cross-sectional study was performed. MED was determined using a handheld device with wavelength of 311 nm. Vitiligo severity was measured using the Vitiligo Area Scoring Index (VASI) while disease activity was assessed by the Vitiligo Disease Activity (VIDA). Sun exposure was quantified by the Sun Exposure Index (SEI).

RESULTS

A total of 36 patients (mean age of 49.06 ± 21.29 years old) participated with 12 patients from each skin phototype. MEDs of skin affected by vitiligo were 255 ± 120.3, 280 ± 93.4, and 525 ± 226.1 mJ/cm2 for phototypes III, IV, and V respectively. The MEDs of unaffected skin were 465 ± 120.3, 580 ± 123.6, and 1150 ± 116.8 mJ/cm2 for phototypes III, IV, and V respectively. The MEDs for skin affected by vitiligo were 45%, 52%, and 54% less than the MEDs of unaffected skin for phototypes III, IV, and V respectively. The differences in MEDs between vitiligo-affected skin and unaffected skin were significant for all skin phototypes (p < 0.001). MED of skin with vitiligo negatively correlated with vitiligo severity, r = -0.426, p = 0.01. There were no significant correlations between MED and VIDA, disease duration, or SEI.

CONCLUSION

MED of skin with vitiligo was much lower than unaffected skin, and MEDs between skin phototypes III, IV, and V differed despite similar depigmentation. MED was not influenced by vitiligo disease activity, duration, or sun exposure.

A Spectrophotometric Method to Determine Minimal Erythema Dose for Ultraviolet Radiation in Human Skin

Background/Objectives: Ultraviolet radiation (UVR) induces oxidative stress in the skin by generating reactive oxygen species (ROS), which can lead to inflammatory conditions including erythema (a sign of sunburn). This clinical study aims to develop an instrumental evaluation method to determine the minimal erythema dose (MED) for UVR. Methods: Fourteen human subjects aged 27 to 57 years (48.93 ± 8.54) participated in this study. Six subsites were designated on the test skin site of each subject and irradiated with UVR at different doses. The examiner visually assessed erythema, determining the 'visual MED'. Additionally, the a* value (a chrominance parameter presenting greenness to redness) was measured using a spectrophotometer as an indicator of erythema. The a* values of the UVR-irradiated subsites were compared to the non-irradiated control value, and the differences were referred to as Δa*. The Δa* value of the subsites irradiated with UVR at the 'visual MED' was referred to as the Δa*VMED for each subject. The mean of the Δa*VMED values of all subjects was chosen as a criterion value for the 'instrumental MED'. The 'instrumental MED' was defined as the lowest dose of UVR that causes an Δa* value equivalent to the criterion value. The 'visual MED' and 'instrumental MED' values of all subjects were subjected to correlation analysis. Results: The mean of the Δa*VMED values of all subjects was 1.88 ± 0.8. The means of the 'visual MED' and 'instrumental MED' values (in J m-2 unit) of all subjects were 300.14 ± 84.16 and 303.29 ± 77.99, respectively. In Pearson correlation analysis, the 'instrumental MED' and 'visual MED' values had a very strong positive correlation with each other (r = 0.864, p = 0.000). Conclusions: This study suggests that the instrumental evaluation method of MED based on the spectrophotometric measurement of the a* values can complement or replace the visual evaluation method and that this method will be useful in monitoring skin tolerance to oxidative stress affected by prooxidant factors and defensive factors.

Evaluating the factors influencing sun protection factors (SPF): Pooling data from multiple studies involving two reference ISO 24444:2019 sunscreen products (P2 and P8)

BACKGROUND

Standardized methods for sun protection factor (SPF) testing are still beset with endpoint and method-driven issues, and can be influenced by multiple factors. The purpose of this analysis is to explore the factors influencing the results of sun protection factor (SPF) testing in human subjects according to the ISO 24444:2019 standard. Intrinsic factors, such as baseline skin color, age and gender, the minimal erythemal dose on an unprotected area (MEDu), as well as environmental factors such as season/weather influences, are considered for analysis.

METHODS

Datasets generated for two reference products (P2 and P8) during the conduct of 50 such studies using the ISO standard 24444:2019 for the testing of SPF products, from a single testing center located in Bucharest, Romania between April 2021 and December 2022, were retrieved and compiled. Overall, the data for 334 subjects was available, with 276 observations for the reference P8, and 171 for P2.

RESULTS

No effects due to gender or age were detected. Seasonal changes, the individual typology angle (ITA°) and MEDu were found to have an influence on the outcome of the SPF values.

CONCLUSIONS

This study adds new original data about the impact of intrinsic and extrinsic factors on SPF variations pertaining to ISO reference sunscreen P8 (SPF 50+). The findings suggest that some factors will inevitably impact the results between two SPF experiments for the same product and SPF testing laboratory. The interconnections between the sources of this variation are discussed. The findings of this research help to identify and characterize factors that contribute to SPF testing variability.

Circadian Oscillations of Minimal Erythema Dose (MED) are Also Influenced by Diet in Patients with Psoriasis: A Chronomedical Study

INTRODUCTION

Minimal erythema dose (MED) remains a parameter of paramount importance to orient narrow-band (NB)-UVB phototherapy in psoriatic (PsO) patients. Recently, circadian rhythm and diet were recognized as potential MED modulators, but their mutual interaction remains understudied. Thus, we aimed to evaluate the potential diet modulation of MED circadian oscillations.

METHODS

In the first phase, a cohort study was performed comparing potential MED oscillations (morning, afternoon, and evening) among omnivorous psoriatic patients before and after a phototherapy cycle and omnivorous healthy controls. The two groups were age-, gender-, skin-type-, MED-, and diet-matched. Then, in the second phase, another cohort study was carried out comparing MED oscillations 24 h after the last phototherapeutic session only in psoriatic patients cleared with NB-UVB and undergoing different diets (vegan, vegetarian, paleo , ketogenic, intermittent circadian fasting, and omnivore). Patients with different diets were age-, gender-, and skin-type matched.

RESULTS

In the first phase, we enrolled only omnivores, specifically 54 PsO patients and 54 healthy individuals. Their MED before and after NB-UVB therapy changed significantly among the three different time-points (morning, afternoon, and evening) (p < 0.001). The time effect was statistically significant in both groups before and after phototherapy. In the second phase, we enrolled 144 PsO patients (vegan, vegetarian, paleo, ketogenic, intermittent circadian fasting, and omnivore). MED circadian oscillations preserved a significant difference also after clearance and were influenced by diet type and time of day (p < 0.001). In particular, vegans displayed the lowest MED values, whilst Ramadan fasting showed the highest values in morning, afternoon, and evening.

CONCLUSIONS

Diet, like other ongoing therapies, should be reported in the medical records of patients with psoriasis undergoing NB-UVB and patients with lower MEDs should be preferentially treated in the morning when the MED is higher.

Validation of a novel method of ultraviolet-induced cutaneous inflammation and its associations with anhedonia

Affective immunology of the skin is a growing area; however, established protocols for measuring individual differences in cutaneous inflammation are lacking. To address this, we present a preliminary validation of Precision Implementation of Minimal Erythema Dose (PI-MED) testing as a method for measuring cutaneous inflammation. PI-MED is a recently adapted protocol, optimized for reproducibility and individual differences research, that uses ultraviolet (UV) light to evoke cutaneous erythema, or inflammatory skin reddening. PI-MED's novel UV dosage schedule produces standardized erythema responses across different skin pigmentation types and shows strong internal consistency within person and good test-retest reliability across 8-10 weeks. In line with predictions, increased PI-MED erythema was associated with heightened anhedonia, across several measures, beyond influences of non-affective covariates. While future work should further refine the dosage schedule for the lightest and darkest skin types, overall, evidence supports PI-MED as a protocol for inducing and measuring individual differences in cutaneous inflammation. Further, PI-MED-induced erythema can expand psychoneuroimmunology research by offering a complementary assessment for general inflammatory tone. This work adds to a growing body of evidence demonstrating a distinct relationship between inflammation and anhedonia.

Commentary: Facial Aesthetic Dermatological Procedures and Photoprotection in Chinese Populations

The medical literature on aesthetic dermatology has primarily focused on a light-skinned patient population, yet patients of darker skin types have different needs and priorities. In Chinese individuals, key concerns include altered pigmentation, which is perceived to age the individual, and also relates to the Chinese cultural standard of beauty of fair skin; many seek aesthetic treatment for this. Non-invasive cosmetic procedures such as lasers and injections are also gaining in popularity in the Chinese market, but this population is prone to hyperpigmentation as an adverse effect of such procedures. Considered and tailored approaches, both to primary concerns of photoaging and the side effects of cosmetic treatments, are warranted.

Skin biophysical properties including impaired skin barrier function determine ultraviolet sensitivity

BACKGROUND

The levels of burning susceptibility to ultraviolet (UV) radiations are affected by various factors, including Fitzpatrick skin types, skin color, sex, and ethnicity. However, studies on the relationship between skin biophysical properties and erythemal responses to UV radiations are rare.

OBJECTIVE

This study aimed to investigate biophysical properties of the skin that determined individual skin sensitivity to UV radiation.

METHODS

As an indicator of skin sensitivity to UV radiation, Korean women were subjected to minimal erythema dose (MED) testing. The skin biophysical properties, such as skin hydration, transepidermal water loss (TEWL) were measured. MED were also evaluated in further variations in the skin, including barrier disruption.

RESULTS

A significant negative correlation was observed between TEWL and MED. With an increase in TEWL, that represents reduced skin barrier function, skin UV sensitivity also increased. Artificial alteration of skin conditions also changed erythemal response to UV radiation. When the skin barrier was disrupted, MED significantly decreased, indicating increased skin UV sensitivity. It is hypothesized that the altered penetration of UV radiation into the stratum corneum under the respective skin conditions caused different erythema reactions.

CONCLUSION

For the first time in a clinical study, the skin biophysical properties, including skin barrier function, were found to have significant effects on skin sensitivity to UV radiation. This finding could help predict individual susceptibility to UV damage. Therefore, skincare products that improve skin conditions associated with UV sensitivity, as well as sunscreen are important for protection against the hazards of UV radiation.

Chinese women with melasma exhibit a low minimal erythema dose to both UVA and UVB

BACKGROUND

Melasma is a common disorder manifested by symmetric hyperpigmentation of sun-exposed skin. Although ultraviolet (UV) radiation is a known risk factor of melasma, whether skin sensitivities to UVA and/or UVB differ between healthy controls and female patients with melasma is unknown.

METHODS

Minimal erythema dose (MED)-UVA and MED-UVB results were compared between female patients with melasma and healthy controls. Additionally, relationships between MED values and Melasma Area and Severity Index (MASI) scores, and skin color were assessed.

RESULTS

The melasma and control groups included 142 and 137 subjects, respectively. Compared with healthy control group, our melasma group had lower MED-UVA (P < .001) and MED-UVB (P < .05). MASI scores were negatively correlated with MED-UVA and MED-UVB (P < .001). Additionally, Skin a* values in melasma-involved skin were negatively correlated with MED-UVA (P < .05). Skin b* values in melasma-involved skin were negatively correlated with MED-UVB and MED-UVA (P < .05).

CONCLUSIONS

Patients with melasma exhibit a low MED to both UVA and UVB, rendering them have a predisposition to an increased UV sensitivity. Because of the association between melasma and UV sensitivity, sun exposure should be avoided to alleviate or prevent melasma.

Erythemal and vitamin D weighted solar UV dose-rates and doses estimated from measurements in mainland France and on Réunion Island

Solar UV radiation causes beneficial and detrimental changes in human health. International and national Health agencies recommend avoiding sun exposure when the solar rays are strongest (typically 2 h before and after solar noon). In this study we detail and refine such recommendations. We estimated biologically-effective radiation (inductive of erythema and pre-vitamin D) using spectral solar UV radiation measurements on a horizontal plane at three French sites equipped with spectroradiometers: Villeneuve d'Ascq (VDA) (North of France); Observatoire de Haute-Provence (OHP) (French Southern Alps); and Saint-Denis de La Réunion (SDR) on Réunion Island, in the Indian Ocean. These sites are very different: VDA is a semi-urban site in a flat region, OHP a rural mountainous site and SDR a coastal urban site on a small mountainous island. Biologically active radiation was analyzed by studying erythema induction and measuring pre-vitamin D synthesis. Dose-rates, doses and times for sunburn induction and vitamin D production were derived. Regarding the level of vitamin D dose considered here (1000 IU), we found that at mainland sites time required for vitamin D synthesis was relatively long, even around solar noon, in winter months this could be 2-3 h for phototype II individuals exposing their face and hands. In the tropics vitamin D could always be synthesized in a reasonable time (e.g. 20 min in winter). By contrast, in summer, the required duration times (exposing face, hands, arms and legs) are very short, approximately 2-4 min on the mainland and 1 min in the tropics for phototype II individuals. In all skin phototypes the duration of sun exposure required to induce erythema was generally longer than that to produce vitamin D. These quantitative results, obtained using an instrument measuring on a horizontal plane and with an unobstructed view, do not represent realistic values for human exposure. To account for realistic human body exposure, received doses and times of exposure were adjusted. Our study shows that, mostly in summer, the time periods where limited solar exposure is recommended should be extended, especially at low latitude locations.