[Academic Presentation] Damage to and Repair of the Skin Barrier Induced by Various Phototherapy Modalities

Intense pulsed light (IPL) devices emit broad-spectrum light with wavelengths ranging from 500 to 1,200 nm. By selecting specific wavelength ranges through filters, the light can be absorbed simultaneously by three major chromophores in the skin—hemoglobin, melanin, and water—during a single treatment session. This leads to clinical improvements in pigmentation and erythema, as well as increased synthesis of extracellular matrix proteins and new collagen, resulting in visibly rejuvenated facial appearance. Vogl et al. reported that one month after four treatments, there was no statistically significant difference in skin hydration levels compared with baseline, likely due to thermal effects and mild epidermal thermal injury induced during therapy, which may have contributed to transient moisture loss. However, over time, as the epidermis undergoes natural turnover and repair, skin hydration typically recovers or even increases. Follow-up at one month revealed a reduction in sebum content, suggesting that IPL therapy can be beneficial for patients with excessive sebum production; conversely, individuals with dry skin should use oil‑based skincare products both during and after treatment. IPL therapy can increase skin hydration and enhance the skin barrier function, potentially reducing sebum secretion, while exerting minimal impact on skin tone. Goldberg et al. documented the clinical outcomes and ultrastructural changes observed in photoaged skin following combined irradiation with 633‑nm and 830‑nm LEDs. Histopathological analysis of five subjects demonstrated marked improvement in wrinkles, with electron microscopy revealing thickened dermal collagen fibers. Russell et al. employed the Omnilux LED system to treat 31 patients with facial wrinkles using 633‑nm and 830‑nm LEDs; after nine sessions, wrinkles in photoaged areas showed significant improvement. In another clinical study, 93 patients with photoaging were treated with 590‑nm LEDs, yielding results indicating that 90% experienced amelioration of photoaging signs, with notable improvements in periorbital wrinkles, overall skin texture, erythema, and pigmented lesions. Collectively, these studies demonstrate that intense pulsed light harnesses photothermal and penetrative effects to stimulate metabolism, accelerate blood circulation, and improve skin appearance, resulting in noticeably smoother skin. Nevertheless, factors such as individual patient sensitivity, operator skill, and treatment parameter settings may lead to temporary adverse reactions like erythema or edema, which can be promptly managed with simple cold sprays, compresses, or reparative masks. Prior to treatment, it is imperative to address compromised skin barrier integrity, provide thorough training for practitioners, and carefully optimize treatment parameters.

Han et al. observed that after erbium laser treatment, the stratum corneum exhibited a high water content; by one week, epidermal scabbing had occurred, the stratum corneum had thickened, and its water content had decreased. As the wound gradually healed, the water content once again returned to normal levels. In contrast, following irradiation with a long-pulse 1064 nm Nd:YAG laser, the water content increased by only 1.2% compared with the non‑laser‑treated group, and no significant difference was evident after one week. Subsequently, the water content began to rise and surpassed that of the non‑laser‑treated group, suggesting that laser resurfacing can enhance the skin’s barrier function. Trans‑epidermal water loss (TEWL) primarily comprises sweat secretion and water evaporation and is closely related to the functional state of the stratum corneum. Immediately after erbium laser irradiation, TEWL increased significantly; similarly, following long‑pulse 1064 nm Nd:YAG laser exposure, TEWL rose by 159 μg/m²·h, likely due to laser‑induced edema and functional alterations in the stratum corneum. Thereafter, TEWL gradually declined, eventually falling below the control area. Notably, in the long‑pulse 1064 nm Nd:YAG–irradiated region, TEWL returned to baseline earlier than in the erbium‑laser‑treated area, indicating that the impact of erbium laser on the skin barrier persists longer, with slower recovery and more pronounced effects. By contrast, mice treated with the long‑pulse 1064 nm Nd:YAG laser demonstrated superior skin barrier function.

Brightman et al. found that the dermal hydroxyproline content in areas treated with both a fractional laser and a long-pulse 1064 nm Nd:YAG laser was significantly higher than in their respective control groups, indicating that both laser modalities strongly stimulate new collagen synthesis. Moreover, the erbium laser proved more effective than the long-pulse 1064 nm Nd:YAG laser in promoting collagen production. Dermal thickness varies with age: before the age of 20, the dermis gradually thickens, whereas after 20, it progressively atrophies, leading to a reduction in dermal thickness. Both the erbium laser and the long-pulse 1064 nm Nd:YAG laser can safely and effectively enhance skin elasticity, dermal thickness, collagen content, and skin barrier function. The erbium laser elicited greater collagen synthesis, more pronounced increases in elasticity, and greater gains in dermal thickness; however, the long-pulse 1064 nm Nd:YAG laser resulted in a more substantial increase in skin hydration. In terms of improving transepidermal water loss, the two lasers were comparable.

Ultra-short pulse lasers primarily induce plasma‑induced ablation, which arises from the electro‑ionic effects of the plasma itself. Because this process occurs extremely rapidly, only a minimal amount of energy is transferred to the surrounding tissues, resulting in very limited thermal damage to adjacent structures. Wanner Studies investigating Q‑switched ruby laser treatment for secondary pigmentation have shown that, one week after irradiation, melanin hyperplasia is observed near the hair follicles, and by five weeks, a redistribution of pigment‑containing cells is evident around basal and spinous cells. However, post‑inflammatory hyperpigmentation is considered transient, with gradual fading of the pigment occurring within two months following laser therapy.

With the advancement of medical optoelectronic technologies, photonics has been extensively applied in clinical practice, enabling effective treatment for many refractory, disfiguring skin conditions. However, during these procedures, the skin barrier is invariably compromised to varying degrees. The extent of barrier disruption and subsequent repair following phototherapy is influenced by the patient’s pre‑treatment skin condition, the specific parameters of the phototherapy modality, and the use of post‑treatment reparative products. Therefore, timely and objective assessment of skin barrier function, selection of appropriate treatment parameters, and judicious application of reparative agents can facilitate faster and more robust restoration of the skin barrier.