The original Snapchat logo consisted of a smiling ghost on top of a glossy yellow background, in the style of Apple's famous "skeumorphism" of the era.
In June 2013, the ghost icon lost its face as a part of a large update for the app. In September 2013, the glossy background was replaced with a gradient, and the shadow behind the ghost was removed. In around October or November 2014, the gradient was removed, making the background a pure flat yellow.
In August 2019, the ghost's outline was substantially thickened, which has also led the icon to subtlely change shape.