Ptaquiloside,a carcinogenic chemical is found in both the bracken fern and its spores. It has been shown that the spores can cause cancer in mice and bracken has been linked to bladder and intestinal cancer in cattle and horses as well as a number of
diseases in other farm animals. It has also linked to human gastric cancer where people, particularly children, eat dairy products where bracken has formed a significant part of the cows diet. In some cultures bracken has been used as a food for humans
being eaten fresh, or preserved, in making bread, brewing beer, and the starch from rhizomes used to make flour and confectionary. It has been implicated in human bladder esophageal and stomach cancers.
health and safety terms while bracken may be a hazard to humans there does not appear to be any firm evidence, yet, that it presents a significant risk to humans. However, it is better to take reasonable precautions.
Physical contact with bracken during harvesting, heaping and turning should be minimised, particularly in late August - October when it may be sporing. However, the Forestry Commission has, due to conservation restrictions, cut and composted
bracken in September and later in the year when it is lignified and drying out. An advantage of a September cut is that there is low or negligible Ptaquiloside present.
One of the factors that reduce the risk of ingesting the spores
is that bracken only spores at intervals of about ten years. The spores are found in a thin strip on the curled-over edge of the underside of the fronds but do not usually extend to the extreme tip of the leaflet.
a facemask should be worn when handling the plant. The use of gloves to protect the hands is a sensible precaution at any time of year as pulling up bracken stems by hand can result in cuts.
Bracken may also harbour sheep ticks, which may, carry Lime
Disease, so it is sensible to check exposed areas of skin after working with bracken