Where is the highest concentration of capsaicin found within the structure of a chili pepper?

The seeds and the white inner pith (placenta)

When an individual seeks to reduce the heat level of a chili pepper, whether for culinary reasons or to manage digestive discomfort, targeting the primary source of capsaicin is the most effective strategy. The chemical responsible for the burning sensation is not distributed evenly throughout the pepper's flesh. Instead, the highest concentration of capsaicin is localized specifically within the seeds and the white, spongy tissue that surrounds them internally, which is technically referred to as the placenta or pith. By carefully removing both the seeds and this white membrane before consumption or processing, a significant portion of the volatile heat compound is eliminated, thus toning down the overall pungency of the pepper substantially.