Background and Purpose Lapatinib, a widely-used dual inhibitor of EGFR/ERBB1 and HER2/ERBB2 effectively targeting HER2 positive breast cancer, has been seriously limited due to cutaneous toxicity. However, the specific mechanism of lapatinib-induced cutaneous toxicity has not been clarified, leading to a lack of effective strategy targets to improve clinical safety. Here, we aimed to identify molecular mechanism occurs in this process and strive for effective intervention strategies against lapatinib-induced cutaneous side effects. Experimental and Approach C57BL/6 mice were subjected to lapatinib via intragastric administration, serum was used for ELISA assay, skin tissue was collected and performed with histopathological analysis. Apoptotic assay was analyzed in HaCaT and NHEK cell lines, comet assay was conducted to measure the damage of DNA, real-time PCR was used to assess the level of HMGB and inflammatory factors. Key Results We found that lapatinib could induce mitochondrial dysfunction, lead to DNA damage and finally cause apoptosis of keratinocytes. In addition, we found that lapatinib could induce aberrant immune response and promote the release of inflammatory factors in vitro and in vivo. Mechanistically, downregulated expression of HMGB1 played a critical role in these toxic reaction processes. Delightfully, we found that saikosaponin A could significantly rescue the reduced HMGB1 transcription, which could alleviate lapatinib-induced DNA damage, inhibit keratinocyte apoptosis and further prevent toxicity of lapatinib in mice. Conclusion and Implications Our study provided molecular mechanism of lapatinib-induced cutaneous toxicity, and shed new light on the prevention of cutaneous adverse drug reactions induced by EGFR inhibitors.