Overcooked charcoal caused an Ash Wednesday health scare in the Philippines, with the bishop ordering an investigation after several parishioners at his cathedral complained about irritation and blisters after receiving their ashes at the beginning of Lent.

The incident took place at San Roque Cathedral in Caloocan City, when Mass-goers receiving ashes from a few of the containers started complaining about adverse reactions on their foreheads.

At first, the diocese was concerned about foul play, and ordered a review of the video footage of the ceremony to see if they could spot any odd happenings. They also sent samples of the ashes to a lab for testing.

“We ruled out the possibility of a sabotage after reviewing the CCTV footages carefully,” Bishop Pablo Virgilio David of the Diocese of Kalookan told CBCPNews, the news agency of the bishops’ conference.

The lab said overcooked charcoal, caused by over-burning the palms used to make the ash, made some of the ashes “caustic,” and it produced an acid when mixed with water before applying them to the faithful.

Most of those affected did not get blisters, since the caustic material rose to the top.

“The rest who got just moist ashes suffered only minor rashes that disappeared as soon as the substance was washed off,” David said.

“What matters for us is that we are able to apply the proper medication – silver sulfadiazine – on people who have been affected,” he said.