If there are negative externalities in production or consumption, competitive equilibrium is unlikely to be Pareto efficient but positive externalities enhance the efficiency of the market.

Pareto Efficient

A scenario in which it is impossible to improve the status of any individual or preference without adversely affecting at least one other individual or preference.

Negative Externalities

Costs suffered by a third party as a result of an economic transaction in which they were not involved, such as pollution.

Positive Externalities

Benefits that affect parties who did not choose to incur that benefit.