Present on the tops of the friction skin ridges are very minute sweat pores that are constantly exuding perspiration. This perspiration adheres to the outline of these ridges. Other substances, like oil from touching your face or hair, can also adhere to these ridges. When an object is touched, a recording of these characteristics may be left upon the surface. At times, these impressions will be visible, and at other times they will be invisible; thus the term “latent”. Although visible prints are truly patent prints, they are frequently referred to as latent prints. The invisible latents must be developed or made visible either by the application of powders, chemicals, or electronic means.