Why can Luffy use fire?

Why can Luffy use fire? Very possibly, it is the friction of air against the gum-like composition of his fist, combined with the speed of stretching his flexible arm, which results in Luffy’s arm igniting into flames to hit his enemies with a hardened, flaming punch.

Very possibly, it is the friction of air against the gum-like composition of his fist, combined with the speed of stretching his flexible arm, which results in Luffy’s arm igniting into flames to hit his enemies with a hardened, flaming punch.