(Kern 1975, p. 95) "In the late 1890s the "bosom ring" came into fashion briefly and sold in expensive Parisian jewellery shops. These anneaux de sein were inserted through the nipple, and some women wore one on either side." Kern, Stephen (1975). Anatomy and Destiny: a Cultural History of the Human Body. Bobbs-Merrill. ISBN0-672-52091-5.
(Parents 2007, p. 151) "Navel piercing. Unlike the other body piercings, this one has not been recorded in history." Parents. Stellan Consult Ltd. 2007.
(Levin 2007) Levin, Liran (June 2007). "Alveolar Bone Loss and Gingival Recession Due to Lip and Tongue Piercing". N Y State Dent J. 73 (4): 48–50. PMID17891882.
Elzweig, Brian; Peeples, Donna K. (2011). "Tattoos and piercings: Issues of body modification and the workplace". SAM Advanced Management Journal. 76 (1): 13–23. ISSN0749-7075 – via Business Source Complete.