Hywel's main research interests are evidence-based dermatology and the epidemiology and treatment of childhood eczema.

In terms of academic impact, Hywel has published over 640 peer-reviewed articles, including papers in Nature, the NEJM, Lancet and BMJ, and three books. He is the second most cited dermatology researcher in the world on Google Scholar (131,513 citations December 2022) with a H-index of 122 and i10-index of 466. His lifetime c-score for 2022 (excluding self-citations) places him in the top 1.3% of the top 100,000 scientists worldwide, the most cited scientist in the Faculty of Medicine at Nottingham and the second most cited scientist in the University of Nottingham. The c-score (Mendeley Data, V5, doi: 10.17632/btchxktzyw.5) focuses on impact (citations) rather than productivity (number of publications) and it also incorporates information on co-authorship and author positions (single, first, last author).