Primeiro falamos sobre o universo no Stargate SG-1 S8E2:
O'NEILL (sitting up with Daniel's help): Getting my head sucked by one of those damned Ancient head-suckers. And something about twins. (He looks at Teal'c.) Teal'c -- what's with the hair?
THOR: O'Neill.
O'NEILL: Thor. You got aspirin?
THOR: You should feel better momentarily and your memory will slowly return. (Jack nods, then looks at Teal'c again.)
O'NEILL: Teal'c -- what's with the hair? (Teal'c opens his mouth but Thor interrupts.)
Claro, Teal'c nunca teve a chance de responder O'Neill.
No entanto, no episódio do Atlantis "Midway", vemos essa troca:
SHORTLY AFTERWARDS. Sam and Teal'c are walking through the city.
CARTER: So, Teal'c, the hair?
TEAL'C: You do not like it?
CARTER: Oh, I love it! It's very ... Earth!
(They smile at each other, then he looks around the area.)
O que talvez nos dê a melhor percepção.
Teal'c vive há muito tempo na Terra, mas não se tornou parte da cultura da Terra.Nós o vemos tentar continuar assimilando em SG-1 S8E7, onde Teal'c consegue permissão para viver da base em seu próprio apartamento. Eu vejo essas duas coisas como um sinal muito claro de que Teal'c está pronto para deixar seu passado dominado por Goa'uld e fazer um lar com os Tau'ri.
Eu também acho que a falta de uma resposta direta no universo nessas duas primeiras citações deve ser uma resposta. Sua mudança era perceptível para todos, mas no geral não era algo que necessariamente precisasse de uma explicação.
Fora do universo, temos um motivo muito claro:
"Finally, after years of behind the scenes begging and badgering, actor Chris Judge got his wish -- and Teal'c got hair. Brad had long-resisted Chris's requests but finally broke down since it seemed this was going to be it, the show's final season. I didn't think it was such a big deal, especially considering Teal'c had undergone other notable changes over the course of the series run. Remember that gold tinge his skin possessed, making him look like he was a professional dancer working an all-night rave? Given the fact that certain scenes from this show's first four episodes were shot out of sequence, Teal'c's hair is somewhat inconsistent -- but I'm sure Chris will tell you it was a small price to pay for not having to shave his head every morning.
(Writer / producer Joseph Mallozzi, in a post at his blog), source GateWorld
Outras entrevistas com Christopher Judge mostram que raspar a cabeça todos os dias para o show foi realmente doloroso, então ele estava pronto para desistir.