Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Prestige Brands Holdings (NYSE:PBH) are trading nearly 12% lower today after the company took an ugly swing and completely whiffed on both its earnings and its forward guidance for the full year.

So what: Wall Street had been expecting revenue of $156.8 million and earnings of $0.39 per share for Prestige Brands' fiscal third quarter. But the company came in with revenue of just $146.2 million (a 9% year over year decline) and $0.30 in EPS. Worse still, Prestige Brands now expects to finish the full year with EPS in the range of $1.48 to $1.52, which is weaker than its earlier EPS guidance of $1.65 and well below Wall Street's $1.67 consensus.

Now what: Prestige Brands blamed the weak quarter on "inventory reductions as a result of soft foot traffic, the return of several competing brands to the marketplace, and a weak cough/cold season." When you can't sustain your momentum once competitors get back in the game, that raises concerns about your value proposition as a company and as an investment. On the other hand, this latest guidance update pegs Prestige Brands' full-year growth at roughly 20% over its last fiscal year. That's still respectable for a company that boasts a P/E of just 15.6. You might want to keep a closer eye on this stock, particularly if it slides further into value territory.

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Alex Planes has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.