In recent years, there has been a noticeable development in oncological treatment, including chemotherapy and biological treatment. Despite their significant effectiveness, they are not free from side effects, such as allergic and dermatological reactions. These reactions can vary in severity and outcome, including potential death. Examples, among others, are type I-IV hypersensitivity reactions of various origins and skin reactions including rashes, itching and redness, but also severe cutaneous syndromes. Due to the therapy used, these may include Stevens–Johnson syndrome, toxic epidermal necrolysis, drug rash with eosinophilia and systemic symptoms, drug-induced hypersensitivity syndrome and acute generalized exanthematous pustulosis. In some cases, it is necessary to interrupt therapy, which may result in a poorer outcome and shorten the patient’s survival. This paper reviews various types of research documents published since 2016. It aims to systematize the latest knowledge and highlight the need for further research into ways to avoid adverse reactions.