Headline inflation decelerated again in May, with consumer prices increasing at an annual pace of 4 per cent, down from 4.2 per cent in April.But trimmed mean inflation, the Reserve Bank's preferred measure of underlying inflation, increased to 3.6 per cent, up from 3.4 per cent in April.Underlying inflation allows economists to look beneath the daily noise of random price movements to see what the economy's broader inflationary pressures are looking like.The Bureau of Statistics says underlying inflation is now running at its highest annual pace since the September quarter of 2024.The RBA has warned that inflation will trend higher in coming months as the fallout from the global energy shock works its way through Australia's fuel prices and supply chains.