Shares of medical skin care company Obagi Medical Products plunged 24 percent on Friday after the company reported a quarterly loss, cut its profit guidance and three analysts downgraded shares.

Much of the decline came after the company disclosed that a regulatory decision in Texas, banning a key ingredient used in several products, is expected to cut sales in that key state.

The Long Beach company late Thurday reported a net loss of $2.4 million (-13 cents per share), compared with net income of $1.9 million (9 cents) a year earlier. Revenue rose 3 percent to $26.5 million, less that Wall Street expected.

Excluding charges, Obagi said it earned 16 cents per share. Analysts surveyed by Thomson Reuters expected per-share profit of 13 cents on $27.1 million in revenue.

The charges included costs for a legal settlement with company founder and former director Dr. Zein Obagi, who sued the company for anti-competitive practices against a more recent company he started, ZO Skin Health Inc. The company also took a sales return provision to account for the impact of a recent decision in Texas to restrict the shipping of products containing 4-percent hydroquinone, an ingredient in several Obagi Medical anti-aging products. Texas accounted for 8.8 percent of the company’s 2010 revenue in 2010.

“We are disappointed by the unexpected position taken by the state of Texas, however we are fully complying with its request to cease shipment of our hydroquinone products in the state,” Chief Executive Al Hummel said in a statement.

For the full year, the company now expects per-share profit between 75 cents and 78 cents per share on revenue between $114 million and $116 million, down from earlier guidance of 87 cents to 91 cents profit on revenue between $119 million and $122 million. Analysts had expected full-year profit of 81 cents per share on $117.7 million in revenue.

Analysts at Robert W. Baird, Needham & Co and Roth Capital cut their recommendations on Obagi Medical’s stock.

Shares on Friday closed down $3.10, or 24 percent, to $9.80 on the Nasdaq.