The p- stands for para-, indicating that the two methyl groups in p-xylene occupy the diametrically opposite substituent positions 1 and 4.

[11] The production of p-xylene is industrially significant, with annual demand estimated at 37 million tons in 2014, and still on the increase.

The p-xylene is then separated out in a series of distillation, adsorption or crystallization and reaction processes from the m-xylene, o-xylene, and ethylbenzene.

Its melting point is the highest among this series of isomers, but simple crystallization does not allow easy purification due to the formation of eutectic mixtures.

Such separation procedures are major cost factors in the production of p-xylene, and the search for alternative methods continues.

Overexposure of p-xylene in humans can cause headache, fatigue, dizziness, listlessness, confusion, irritability, gastrointestinal disturbances including nausea and loss of appetite, flushing of the face, and a feeling of increased body heat.

If skin exposure occurs, first aid includes rinsing and then washing the affected area with soap and water as well as removing any contaminated clothing and thoroughly cleaning and drying before reuse.

[17] Ingestion of p-xylene can result in a burning sensation, abdominal pain, dizziness, drowsiness, headache, and nausea.