Hayden Panettiere Olivia Munn Jessica Alba Hair Extensions

Hayden Panettiere, Oliva Munn and Jessica Alba sport hair extensions. Photos: Theo Wargo/WireImage for Vans | David Livingston/Getty Images | Michael Buckner/Getty Images

When the heat is on, most women opt for shorter, cropped 'dos, but some of our favorite stars are going to great lengths this summer.

"Extensions can be very fun and rewarding," celebrity stylist and Hair Basics expert Ted Gibson tells StyleList. "They can range in price from $500-$5,000 and last from two weeks to four months, depending on which hair extensions you and your stylist decide on."

Hayden Panettiere, who has turned heads with her frequent hair switch-ups, attended the Vans Custom Culture Contest event in New York City on June 2 rocking wavy blond extensions. At the Elizabeth Glaser Pediatric AIDS Foundation benefit on yesterday, Olivia Munn gathered her long, dark lengths into a ponytail and left out a few face-framing pieces. And for the Covenant House California Gala last Thursday, Jessica Alba paired her gorgeous mommy-to-be glow with layered, sun-kissed extensions for a half-up, half-down hairstyle.

Anxious to lengthen your locks like these celebs? Check out the expert advice below on how to style and care for hair extensions.

Not all extensions are created equal. "Always consult with a professional when it comes to hair extensions. You have to try and seek out the perfect extension type suitable for your hair, says Angelo David, celebrity stylist and salon owner. "Human hair extensions (especially Remy Hair) are by far the best, and they have to be customized according to your hair and the look you want to achieve like the Couture Hair Addition services we offer. Regular salon visits are important to keep your extensions in good shape."

Ask and you shall receive. Stylist Peter Santana of Sean Donaldson Hair in Miami, Florida believes there are three questions every pro should pose before you sit down in the chair:
• What look do you want to achieve?
• What length are you looking for?
• What is your face type and body frame?

It's all about blending and layering. "When extensions are applied, it is key to blend them with the client's hair to achieve a more natural look. Never wear extensions at one length. We suggest a lot of layering," recommends Santana. "When cutting the hair, make sure to use a razor but don't overdo it as the hair will look frayed. Be careful how much pressure you put on your hair extensions with accessories -- it can pull them out."

Paddle away. "The most important tool is a professional paddle brush made especially for extensions," says Santana. "It is important to always brush the hair from the bottom up."

Say no to alcohol. "Products are so important to maintaining a beautiful mane of hair," says Amoy Pitters, celebrity stylist that tends to the tresses of Naomi Campbell, Alicia Keys and Sheryl Crow. "Alcohol-based products should not be used. Instead, focus on more oil-based products like shea or argon and a little goes a long way. Too much product will wear your hair down and increase build-up on the scalp."

Don't sleep on at-home hair maintenance. "Before taking a shower, slowly brush your hair upwards to prevent breakage. Use intense hydrating shampoo and conditioners followed by a great detangler and a wide-tooth comb. Apply a leave-in conditioner and let hair air-dry for a summer look, or apply a frizz control product like ANgelo David Zero-Frizz Control when blow-drying to protect it from excessive heat," says David.

Know when it's time to let go. "Keeping extensions in too long can cause major hair or scalp damage," adds Pitters. "I tell my clients to take them out after 10-12 weeks."

Did you know that hair extensions have now become a hot commodity among thieves?