Eponychium

{{Short description|Thickened layer of skin at the base of the fingernails and toenails}}

{{Infobox anatomy

| Name = Eponychium

| Latin = eponychium

| Image = Nail svg hariadhi.svg

| Caption = Nail anatomy, with eponychium labeled as "nail fold".

| Width = 170

| Image2 = Gray943.png

| Caption2 = Longitudinal section through nail and its nail groove (sulcus).

| Precursor =

| System =

| Artery =

| Vein =

| Nerve =

| Lymph =

}}

In human anatomy, the eponychium is the thickened layer of skin at the base of the fingernails and toenails.{{cite book |doi=10.1016/C2014-0-03145-0 |title=Comparative Anatomy and Histology |date=2018 |isbn=978-0-12-802900-8 |editor1-first=Piper M. |editor1-last=Treuting |editor2-first=Suzanne M. |editor2-last=Dintzis |editor3-first=Kathleen S. |editor3-last=Montine }}{{pn|date=May 2025}} It can also be called the medial or proximal nail fold. Its function is to protect the area between the nail and epidermis from exposure to bacteria. The vascularization pattern is similar to that of perionychium.{{cite journal |last1=Sangiorgi |first1=S. |last2=Manelli |first2=A. |last3=Congiu |first3=T. |last4=Bini |first4=A. |last5=Pilato |first5=G. |last6=Reguzzoni |first6=M. |last7=Raspanti |first7=M. |title=Microvascularization of the human digit as studied by corrosion casting |journal=Journal of Anatomy |date=February 2004 |volume=204 |issue=2 |pages=123–131 |doi=10.1111/j.1469-7580.2004.00251.x |pmid=15032919 |pmc=1571248 }} The eponychium differs from the cuticle – the eponychium is made up of live skin cells whilst the cuticle is dead skin cells.

In hoofed animals, the eponychium is the deciduous hoof capsule in fetuses and newborn foals, and is a part of the permanent hoof in older animals.{{cite journal |last=Bragulla |first=H. |date=March 1991 |title=The deciduous hoof capsule (Capsula ungulae decidua) of the equine fetus and newborn foal |journal=Anatomia, Histologia, Embryologia |volume=20 |issue=1 |pages=66–74 |pmid=1877762 |doi=10.1111/j.1439-0264.1991.tb00293.x }}

The word eponychium comes {{ety|gre|ἐπί (epí)|on top of||ὀνῠ́χιον (onúkhion)|little claw}}.