shounen ai focuses more on the relationship between the two characters. Ppl often say it's more "subtle" if that makes sense.
Yaoi is more explicit and sexual. Usually contains the bed scenes and focuses on stuff shounen ai doesn't.
Shounen-ai has more of a shoujo feeling, it has only a confession and maybe a kiss or a heavily (very) censored first time, like in shoujos XD And Yaoi is the real deal, what has to happen will happen lol
Shounen-ai is more like slowburn,, can be read by minors
Yaoi has sex scene(even if it only has sex scene, it's considered as yaoi)
*even if it only has 1 scene, it's considered as yaoi
Shounen ai is pure romance ,the most you can expect is some kiss scenes and blurred up scenes of them doing the deed.Yaoi is like Hentai,the plot is set up for the characters to do it. Sometimes yaoi do have the plot but there is a more clearer depiction of s e x.
BL (Boys Love or romance between two men)
Shounen Ai : BL without smut (sex scenes ) It has no 18+ content.
Yaoi : BL with smut (sex scenes) It has 18+ content.
Whats the difference between shounen ai and yaoi??