I last recommendedthat Fools take a look at consumer-staples company Clorox (NYSE: CLX) back in June. Shares are up about 7% since then, lagging the S&P 500's double-digit advance. Yet that underperformance, combined with a depressed valuation, makes Clorox one of a shrinking number of historically steady stocks that still has room for upside surprise.

As Exhibit A, I submit the company's fiscal-2010 first-quarter results. Registering $1.4 billion, sales declined 1% versus brisk top-line growth in the year-ago period. Sequentially, sales flopped almost 7%. Unfavorable product mix and currency rates, along with a weak market for the company's premium-priced Glad-brand storage and trash bags, contributed to the humdrum performance.

Earnings per share, however, told a vastly different story. Powered by lower commodity costs, annual efficiency initiatives, and price increases, EPS leapt from $0.90 in the fiscal-2009 quarter to $1.11. Yep, that's a 23% gain. In addition, management said that swine-flu fears -- which boosted sales of the namesake line of household disinfectants -- helped fatten the company's profit.

That puts Clorox in the company of other H1N1 beneficiaries, which run the gamut from vaccine-makers Novartis (NYSE: NVS), sanofi-aventis (NYSE: SNY), and AstraZeneca (NYSE: AZN), to drugstore Walgreen (NYSE: WAG) and face-mask manufacturer 3M (NYSE: MMM). Sudden business spikes are hardly a bad thing, but how long can these companies continue to ride high on the hog?

In the case of Clorox, the market's hardly awash in enthusiasm. By the close of trading, shares had risen less than a third of a percent in response to quarterly results. That compares to a 1.6% daily gain for Colgate-Palmolive (NYSE: CL) stock following the oral- and household-care company's recent quarterly report, even though EPS and gross-margin growth were hardly the stuff of the bleach king. What's more, Colgate-Palmolive trades at a 16.3 forward P/E to Clorox's 12.9.

What gives?

I can't divine Mr. Market's exact motivations (although you'll be the first to know should I develop that unique ability), but I'd say that it comes down to product exposure. In fiscal 2009, the cat litter, laundry, charcoal, and trash bag categories pitched in 43% of Clorox's net sales. However, compared to other areas of the company's portfolio, it's these very categories that are most susceptible to consumer trade-down and private label penetration.

That vulnerability came through in Clorox's recent results: Management informed conference-call listeners that overall company market share was down slightly for the quarter, and cited particular challenges in the Glad and laundry businesses.

Investors, it appears, remain spooked, even as the company raised full-year EPS guidance from a range of $4.00-$4.15 to $4.05-$4.20. Continued...