( However ( , ( ( exposure ( to ( ultraviolet radiation ) ) ) ( ( can ( ( ( ( increase ( ( the amount ) ( of pigment ) ) ) ( in ( the skin ) ) ) and ) ( make ( it ( appear darker ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (NP (NP (NN exposure)) (PP (TO to) (NP (JJ ultraviolet) (NN radiation)))) (VP (MD can) (VP (VP (VB increase) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NN pigment)))) (PP (IN in) (NP (DT the) (NN skin)))) (CC and) (VP (VB make) (S (NP (PRP it)) (VP (VB appear) (NP (JJR darker))))))) (. .)))
However, exposure to ultraviolet radiation can  increase the amount of pigment in the skin and make it appear darker.
(ROOT (S (NP (NP (NNP Exposure)) (PP (TO to) (NP (JJ ultraviolet) (NN radiation)))) (VP (MD can) (VP (VP (VB increase) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NN pigment)))) (PP (IN in) (NP (DT the) (NN skin)))) (CC and) (VP (VB make) (S (NP (PRP it)) (VP (VB appear) (NP (JJR darker))))))) (. .)))