The skin acts as a protective barrier, is crucial for thermoregulation and also forms part of the sensory, immunological and endocrine system. Therefore skin preservation is paramount to preserving life. The loss of skin homeostasis, through injury, initiates the wound healing process where the final outcome is the formation of a scar. Scar treatment remains a challenge, despite a plethora of treatments, resulting in a poor outcome and sub-optimal response to existing therapies. Photodynamic therapy (PDT) has been used to treat oncologic conditions affecting the skin. Its action depends on a photosensitiser and a specific light source. Aminolevolinic acid (5ALA) and its methyl ester (MALA) are commonly used pro-drugs of the photosensitiser protoporphyrin IX (PpIX), which in combination with red light produces reactive oxygen species (ROS). ROS will cause different responses such as cell death and tissue destruction. There is limited clinical evidence emerging for the use of PDT in treating wound healing and pathological skin scarring. For this reason, further investigations are required to better understand the role of PDT in adult human skin wound healing and skin scarring. The aim of this investigation was to evaluate the accumulation of PpIX after exposure to 5ALA or MALA, phototoxicity of red light arrengment, citotoxicity, cell death inducction, ROS generation and a gene related analysis post-PDT in keloid fibroblasts compared to normal skin fibroblasts. Optimization of a wound healing organ culture (WHOC) model and evaluation of re-epithelialization, cell death, proliferation, extracellular matrix arreangment (ECM) and a related gene analysis after 5ALA-PDT ex vivo. General histology, cell death, proliferation, ECM rearrengment and a gene related analysis after PDT in skin scarring ex vivo.This investigation found PpIX accumulation higher with MALA compared to 5ALA. Phototoxicity and cytotoxicity was site specific within the lesion and increased proportionately to fluence rates. ROS generation leads to the decrease of cytoproliferation and increased apoptosis and necrotic cell death, COLI, COLIII an HSP70 were found down-regualted. Ex vivo wound geometry, system of support and growth media were optimized in a human wound healing organ culture (WHOC). WHOCs treated with 5ALA-PDT (20 J/cm2), showed an advancing re-epithelialization tongue 3.5 folds longer, which were highly proliferative, showing increased CK14 and p16 levels. The neo-epidermis was fully differentiated and neo-collagen was present. PCNA, p16, COLI, COLIII, MMP3, MMP19 and alpha-SMA were significantly more expressed in the dermis. MALA/5ALA-PDT (40 J/cm2) applied to striae alba, fine line, hypertrophic and keloid scars ex vivo coused an increased of apoptosis while proliferation decreased, matrix components were found to be re-organised, both according to the severity of the scar. COLI and COLIII genetic expression decreased while MMP3 and tropoelastin increased significantly. However, no statistically significant difference was observed between 5ALA and MALA-PDT treatments. In conclusion, this thesis shows that cytotoxicity post-PDT in KD fibroblasts is dependent on the lesional site within the scar, a precursor of intracellular photosensitiser and fluence. PDT in wound healing ex vivo shows increased re-epithelialization and ECM reconstruction and remodelling. Finally, in dermal fibrosis morphological and cellular effects of the application of PDT correlate with the degree and severity of dermal fibrosis. In view of this, PDT may be ideal for treating abnormal skin scarring and improving human cutaneous wound healing.