In British and Irish superstition, people traditionally say “touch wood” after mentioning a hope to prevent bad luck.
The expression is related to the wider English-language custom of knocking on wood. One explanation connects it with pre-Christian beliefs that spirits or supernatural forces lived in trees, so touching wood could call on protection or prevent a boast from attracting misfortune. Another theory links it to Christian relics or the wood of the cross, but no single origin is proven.
The custom is usually performed immediately after a fortunate statement, such as saying that a journey has gone safely or that a family has avoided illness. The speaker may touch a wooden object or, in modern usage, simply say the phrase.
“Touch wood” is especially associated with Britain and Ireland. In North American English, “knock on wood” is more common. Both expressions serve the same conversational purpose, but they are not identical regional forms.