To dye or not to dye - that is the question.

Hair dyeing is not just a necessity for people who want to cover grey hair, but also a temptation for many others who want to make their hair more attractive and fun.

The Cosmetic, Toiletry and Fragrance Association of the United States estimates that close to two out of every five American women and a smaller number of men dye their hair.

In China, more and more people are also finding it necessary, or irresistible, to dye their hair.

Tang, 55, who has grey hair, often dyed her hair black in the past two years. But she no longer does it because her scalp became more and more itchy after each procedure.

Scalp allergy, dermatitis and hair loss are what many fear hair dyeing might lead to. But according to experts, only faulty application and the use of some strong dyes lead to the problems.

According to researchers, it is the p-phenylenediamine, a chemical element in the permanent dye, that can lead to skin irritation and dermatitis for those who are allergic to it.

While there are weaker dyes such as natural dyes and semi-permanent colours, some argue that proper application and the use of a low concentration of permanent dye can eliminate the problems.

Hair rupture can result from faulty hair-dyeing procedures such as dyeing for too long, at a too high temperature or using a highly concentrated dye.

Harm can be done to people's hair if they dye too often.

"Many people these days not only dye their hair but they bleach through the dye with bleach (a hair lightener)," said Gary Pinnegar, a professional hairdresser based in Beijing. "Then they colour it again or colour over the bleach, get bored with that and bleach it again, then the hair breaks off."

As a professional hairdresser, Pinnegar would only dye the new growth using a colour that is not too strong so that the hair won't be damaged.

He also suggests if your hair is dark, not go too blonde, which means using a stronger colour or bleach.

"Stay around your natural colour or go warmer," he suggests.

He explained that's because your hair is a string of dead cells, they are not alive so once damaged they are always damaged until they grow out.

Another concern about hair dye is that it might cause cancer.

Some researchers in the West found that women who regularly use permanent hair dye appear to be at a greater risk of bladder cancer.

The picture is confused because other research findings contradicts these finding.

In 1985 American toxicology experts researched hair dyes and reached the conclusion that in an appropriate concentration, hair dyes have no obvious carcinogenic function or deforming function on embryos.

"Some say it is harmful to health," said Pinnegar.

"But I have worked with colour for years and I seem to be OK.

He suggests people undergo an allergy test before commencing permanent colouring.

Researchers continue to study the cancer-causing potential of permanent hair dye ingredients. Until definitive evidence is found, consumers may want to proceed with caution when considering a dye.