Tumblr has updated its community guidelines.
We now welcome a broader range of expression, creativity, and art on Tumblr, including content depicting the human form (yes, that includes the naked human form).
So, even if your creations contain nudity, mature subject matter, or sexual themes, you can now share them on Tumblr using the appropriate Community Label so that everyone remains in control of the types of content they see on their dash.
– Tumblr