When parties to a contract make promises to perform their obligations, and one party reasonably relies on the other party’s promise—but the party making the promise fails to perform, causing harm or loss to the party who relied on the promise—the party who relied on the promise to perform is said to have relied to its detriment.

This legal concept is called detrimental reliance. Detrimental reliance may serve as a substitute for consideration, and make an otherwise unenforceable contract enforceable.

Thus, detrimental reliance is a legal concept based on fairness (known as equity or equitable), and is equivalent to contractual promissory estoppel (due to the other party’s reliance, the party who did not keep its promise is prohibited from challenging the enforceability of its promise).

Detrimental reliance is not a separate tort cause of action.

In Ohio, the legal concept of detrimental reliance, also known as promissory estoppel, is recognized and can be used to enforce a contract that may otherwise lack consideration and be unenforceable. This doctrine applies when one party makes a promise that the other party relies upon, and as a result of this reliance, the latter party suffers a detriment or loss. Ohio courts will consider several factors to determine if promissory estoppel should apply, including the reasonableness of the promisee's reliance and the foreseeability of the detriment. The purpose of this doctrine is to prevent injustice by prohibiting the promisor from arguing against the enforceability of the promise if the other party has relied on it to their detriment. It is important to note that detrimental reliance is not an independent cause of action for a tort claim; rather, it is a principle of equity that can make an otherwise unenforceable promise binding in the context of contractual relationships.