Alright, see right here before he used kamui, his face and hair should of been burned:
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Madara had a smaller version on his back for s long as Obito did too.
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before Obito kamui-ed it to other dimensions, and like-wise Madara took off his armor.
Both the Uchiha's are suppose to have burned hair...
My solution is that with senju dna, they were able to heal that quickly.
Your entitled to believe whatever you want, i'm just saying what makes sense to me.