The most critical component of the TDDS is the adhesive, which is responsible for the safety, efficacy and quality of the patch. For drug delivery to successfully occur, the patch must adhere to the surface of the contact area. If a patch has inadequate adhesion, it is likely to fall off before the entire delivery period has been satisfied, leading to risks for the patient and others who may encounter the patch. Despite the critical concerns associated with the adhesive properties of the patches, the adhesion quality and failure mechanisms have not been fully studied. If certain molecules encounter the adhesive, it may cause irreversible altering of its chemical composition, which could render it unsuitable for transdermal applications. In many cases of TDDS failure, sweat is believed to be a culprit responsible for causing adhesive failure. The goal of this project is to investigate the chemical composition of the adhesive layer of a transdermal patch. The patch sample is a Sandoz Estradiol Transdermal System manufactured by Noven Pharmaceuticals, Inc., designed to deliver 0.1mg per day and contains 1.56mg of Estradiol USP, the active ingredient. By analyzing the chemical composition of a patch that has not been worn, versus a patch that has been worn, it may be possible to determine the chemical interaction that causes adhesive failure. Fourier Transform Infra-Red (FTIR) Spectroscopy (OPUS FTIR Spectrometer) was performed on an unused estradiol TDDS patch immediately after opening, and again after 24 hours in ambient air to investigate the potential for oxidation. The IR Spectrum was then analyzed, and the peaks were reviewed. The IR Spectra for the sample left out for 24 hours indicated lengthened peaks corresponding to C=O, C-O, and O-H, a decreased transmittance, and a wider bandwidth in those regions. Based on these results, it can be determined that oxidation does occur on a patch sample that is exposed to ambient air. In future works, additional patch samples will be collected and used for an extensive IR and UV analysis. By comparing the IR and UV Spectrum graphs of “used” patches that did not fail, with “failed” patches, it may be possible to identify a cause for premature patch failure related to sweat interactions.