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Cutaneous Photosensitization
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Photobiology is the study of the responses of living systems to irradiation with light. The responses of biological systems to light are based on chemical reactions initiated by the absorption of light by molecules in the system. This is consistent with the first law of photochemistry, which states that light must be absorbed for a photochemical event to occur.1
Mucocutaneous Side Effects
Published in Ayse Serap Karadag, Berna Aksoy, Lawrence Charles Parish, Retinoids in Dermatology, 2019
Tugba Kevser Uzuncakmak, Ayse Serap Karadag
Retinoid associated photochemical reactions are an issue of concern in several research fields including photochemistry, spectroscopy, and photobiology (35). Such reactions may be classified as photoisomerization, photopolymerization, photooxidation, or photodegradation and may present as photoallergic, photoirritant, and phototoxic clinical responses. The knowledge about the exact mechanism is very limited; however, many patients complain about a decreased tolerance to UV radiation shortly after sun exposure during treatment with retinoids (36). Such photosensitivity is more common with isotretinoin and etretinate and probably is related to the reduction in the thickness of the stratum corneum. Also, the incidence and severity of these reactions are dependent on different factors, including the type of product, vehicle, retinoid concentration, dosage and wavelength of the light, and photoirradiation time (35,36).
Photosensitivity and Photoreactions
Published in Gabriella Fabbrocini, Mario E. Lacouture, Antonella Tosti, Dermatologic Reactions to Cancer Therapies, 2019
Cecilia A. Larocca, Mackenzie Asel, Mario E. Lacouture
Classification of photoreaction type often relies on key clinical and histologic features described next (Table 4.1) (1–4). The most common mechanism of skin injury is a phototoxic reaction. Additional subtypes of photosensitive eruptions include photo-induced onycholysis, pseudoporphyria, and photoallergy (1). However, there may be significant overlap among eruptions. Additionally, drugs that induce phototoxic eruptions may also cause photoallergic eruptions. It is likely that other mechanisms of photosensitivity exist, as novel targeted agents and immunotherapies induce photosensitivity eruptions that challenge current concepts in photobiology. As such, in this chapter agents will be broadly referred to as photosensitizers when the mechanism of the eruption is unknown.
Efficacy of pulsed high-intensity laser therapy on pain, functional capacity, and gait in children with haemophilic arthropathy
Published in Disability and Rehabilitation, 2018
Shamekh Mohamed El-Shamy, Ashraf Abdelaal Mohamed Abdelaal
Laser therapy is generally believed to alter cellular and tissue function depending on the characteristics of the laser itself (e.g., wavelength and coherence).[31] The pulsed Nd: YAG laser has a wavelength of 1064 nm and works in a therapeutic window that allows it to penetrate and spread more easily through tissue since human skin does not have an adequate concentration of endogenous chromophores to efficiently absorb this wavelength.[32] Absorption at the tissue level is characterized by light diffusion in all directions (the scattering phenomenon), which increases the mitochondrial oxidative reaction and subsequently increases adenosine triphosphate (ATP), RNA, and DNA production. These so-called photochemistry effects result in the phenomenon of tissue stimulation, also known as the photobiology effect.[32]
Assessing the impact of low level laser therapy (LLLT) on biological systems: a review
Published in International Journal of Radiation Biology, 2019
Ruwaidah A. Mussttaf, David F. L. Jenkins, Awadhesh N. Jha
It is being suggested that the key underlying mechanism of action for most of the physiological effects attributed to LLLT is the stimulation of mitochondrial activity (Hashmi et al. 2010a; Di Giacomo et al. 2013). The first law of photobiology states that photons of low-power light must be absorbed by electronic absorption bands belonging to chromophores to produce significant effects on living biological systems (Huang et al. 2009). A chromophore (or photoacceptor) is a molecule of a compound, which imparts some colour to the compound (Huang et al. 2011).