I can usually tell when I do because my hair will look flat and not curl the way it normally does. If I have a build up of oils (cause I sometimes use oils) it will look greasy and have some straighter spots than others. Once I clarify, I feel like the products work much better and my hair just feels "lighter", if that makes sense.
I can feel it. My hair will feel somewhere between greasy and gritty, like it has very fine... stuff... stuck to it. It will also look greasy down by the roots, but a dull kind of greasy. I also definitely notice dull color -- I have auburn hair, so it's very easy to tell when it suddenly looks brown.
Just throwing this out there: my hair also gets easily overmoisturized, which does not feel greasy, but instead looks shiny and healthy - but with no body or bounce. I confused this with build-up for a while. Now I can tell the difference.
My hair will feel coated and dry, with very flat roots and buildup on the scalp. I hate clarifying, cuz I have to work my way up to fabulous juicy hair again (normally 2-3 days), but it's a must 1-2 times a month...
3B, Fine, Normal P, Normal E, Low-Med D
LowP: Kinky Curly Come Clean (50% EVOO)
NoP: As I Am CC
RO: Suave Coconut, VO5 Shea Cashmere
LI: KCKT or CJBCLI or HETT/HENOYF (w/ 8 drops GSO)