According to an article in the Guardian:
Out of 2,200 men and women, only 18% knew they should replace their pillows every two years. The average person uses the same pillow for three years and two months.
Many – though not all – sleep experts say that if you fold your pillow in half and it doesn't spring open straight away by itself then it's dead: it can't support your head and neck, so bin it.
Are there studies that support the notion that people who only replace their pillows every three years and two months or wait even longer to replace their pillows are likely to suffer from negative health effects as a result?