With the rise in temperature, the ionic-product of water increases, hence $ p{{K}_{\omega }} $ decreases $ \left( p{{K}_{\omega }}=\log \frac{1}{{{K}_{\omega }}} \right) $ . We know that, $ pH+pOH=p{{K}_{w}} $ Hence, pH of solution also decreases with increase in temperature. Hence, at body temperature $ \left( 38{}^\circ C \right) $ the pH of neutral solution will be approximately 6.8.