Abstract: A skin penetration device (2, 102, 202, 302) for administering a test substance (10). The skin penetration device has a first layer (4, 104, 204, 304), a second layer (6, 106, 206, 306), and a third layer (12, 212, 312). It may also have a fourth layer (16, 116, 216). The second layer has a protrusion (8, 108, 208, 308) providing a hollow space for containing the substance to be administered. In The skin penetration device further has a skin-piercing component (18, 118, 218, 318) that can release the substance and rupture the skin when pressed towards the skin in use. The skin-piercing component has a rest configuration and is configured to be biased towards the rest configuration such that it may be deformed but returns to the rest configuration when the deforming force is removed.