Ethylbenzene, which is always co-present except in xylene obtained by the disproportionation of toluene, adds further complications owing to the closeness of its boiling point to that of m- and p-xylene. Crystallization techniques, which take advantage of the range of melting points to separate the xylene isomers, are usually directed towards the isolation of p-xylene. Xylenes have increased their importance as chemical raw materials, with effort directed to improve both process yields and catalyst life and to the use of larger reactors. Xylene is obtained from aromatic-rich streams from refineries or as a by-product of naphtha cracking. The largest outlet for xylenes is as a gasoline octane improver. Chemical uses for the xylene isomers are in the plastics and fibres markets, each isomer having one major outlet. The absorption of xylene takes place chiefly by breathing the vapours which causes irritation to eyes, nose and throat.