The company would not disclose the terms of the agreement, but it has been reported to involve a settlement of some $10m (£6.9m), and a clause preventing P&G from using the information it gained to its advantage.
In a statement, P&G chairman John E Pepper said, "We believe the agreement protects both P&G's and Unilever's business interests. I have been personally involved in ensuring that none of the information has been or will be used in any P&G plans."
P&G hired a corporate intelligence firm to examine Unilever's haircare business, but alerted its rival when the firm went too far in gathering sensitive information.
Unilever's haircare brands include Sunsilk and Organics, while P&G makes Pantene and Vidal Sassoon.
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