The tradition of rubbing ash on the forehead of worshippers is being replaced with the ashes being sprinkled because of Covid-19 concerns.
The change is being made at Chichester Cathedral's Ash Wednesday service, which marks the beginning of the season of Lent.
To comply with Government rules, the Chichester congregation will not have the ash rubbed on to their forehead - instead the clergy will sprinkle it with their hands from a distance over the worshipper's head.
Other restrictions now in place during the cathedral's services include a limit on 40 people attending and the communion wafer being brought to the worshippers as they sit down and it being dropped into their hand rather than being placed.
All of the congregation at the service, which is being broadcast online, are also required to sit socially-distanced and to wear facemasks, with no congregational singing allowed.
The Dean of Chichester Cathedral, the Very Reverend Stephen Waine, said: "Chichester Cathedral remains open and we have made a number of changes to ensure our community can visit us safely at this difficult time - whether that be for prayer, reflection or for services.
"Ash Wednesday marks the start of Lent, an incredibly important time in the Church's calendar as we prepare for the Easter celebration.
"Although the numbers who can join us in person are restricted, we welcome hundreds of more people online through live-streamed services."
During a traditional Ash Wednesday service the repentance ashes are placed on the foreheads of the congregation while the words "Repent, and believe in the Gospel" or "Remember that you are dust, and to dust you shall return" are spoken.
The ashes are prepared by the burning of palm leaves from the previous year's Palm Sunday celebrations which mark Jesus' arrival into Jerusalem.