So, i’ve rigged and animated my character, and I’m making the hair, and even though I’m
in object mode, any movement and size change I do with my hair gets included in animation without my consent and without me even adding keyframes. I’ve tried every mode and stuff but it keeps doing it.
Any solutions?
have you checked if auto keyframe is on?
No, it isn’t on.
It might have some hidden keyframes that I accidentally added near the start,
but I can’t see any.
Kind of hard to see your file if you don’t upload it. Can you upload a file to trouble shoot it? You can strip out materials and unneeded parts to just show what you are talking about.
¿Do the hair has got Bones, Hooks or any other sort of Parenting to the character or Armature Objects?
I suspect you might have accidentally Kayframed one or more hair element’s settings, but you can fix this by checking each one of them while navigating in the Properties Editor.
Also, you might also check in your Timeline/Dope Sheet Editor (maybe Graph Editor as well) your channels for unexpected Keyframes; scroll down, maybe there are stuff there you’ve created but are not aware of.
Another wild possibility could be Modifiers or Bone Constraints related to the hair. Those stuff might be on any of the Objects (even on the Armature) or on the Bones.
And, naturally, there is Weight Paint. Maybe you’ve got wrong Weight Paint on the hair. This shouldn’t be difficult to verify; you have an Armature, so it’s plausible that accidentally you’ve got the same Bones from the body mesh Object affecting simultaneously the hair mesh Object.
It may also help to make sure you have All channels visible- by default, it’s only selected objects that show keyframes, so I wouldn’t be surprised if it looks like there aren’t any keyframes but there actually are 
Great tip, and nice to know. Thank you for complementing.
I’m currently not familiar enough with that Channels concept.