Computational studies on light‐tissue interactions in medical treatment and diagnosis have offered deeper insights in the processes underlying laser treatments and fluorescence measurements. I apply this approach in the study of fluorescence detection and of laser therapy. First, I investigate three methods of fluorescence detection and the reported contrast between healthy skin and malignant tissue. I varied the concentration of haemoglobin in the target, the concentration of melanin in the epidermis, the scattering of light in the skin, the depth at which the target is located in the skin, the width of the target, the thickness of the target, the concentration of photosensitizer in the target, and the concentration of photosensitizer in the skin. My findings confirm previous clinical studies in that the auto‐fluorescence corrected fluorescence detection method generally shows a higher contrast than the other methods. The results support earlier clinical studies and are in accordance with expert experience. Second, I study laser therapy for psoriasis. In a series of simulations, I analyse three types of pulsed dye laser systems and one IPL system. The investigated biological effects are heat shock proteins, hyperthermic tissue damage and vasoconstriction of the microvasculature. The changes in the skin concern blood volume, blood oxygenation and scattering in the epidermis. The calculations show that there are some notable differences in the effect changes in the composition of psoriatic tissue has on the efficacy of laser and IPL therapy. Still, Inter‐device variance was more prominent than intra‐geometry variance. My study adds to the understanding of fluorescence detection of keratinocyte skin cancers, as well as that of laser therapy for psoriasis. Additionally, it offers potential avenues for increasing the efficacy and efficiency of these therapies.