Alyssa is the daughter of Italian-American parents Lin, a former fashion designer and talent manager, and Thomas Milano, a film music editor and a well-known boating enthusiast. She has a younger brother, Cory (born in 1982), who is also an actor, but has more recently started a band, called Chloroform Days, in which he is the lead singer. Alyssa grew up in Staten Island and was raised Catholic. She began her career at the age of eight when she won a part in an open audition for a national tour of Annie. She appeared in television commercials and off-Broadway productions. At the age of eleven, she earned her first major role in the TV show Who's the Boss?, in which she starred as Samantha Micelli, the daughter of Tony Danza's character. When Alyssa won the role, her family relocated from Staten Island to Hollywood. In 1985, she was in the film Commando as Jenny Matrix who was the daughter of Arnold Schwarzenegger 's character. A few years later this film was shown in Japan prompting a producer to offer Alyssa a five album record deal.

After Who's the Boss, however, Alyssa slowly disappeared on America's eyes except her small roles on TV-Movies, but the downward direction of her career came to a stop when Alyssa got breast implants. After the operation, she decided to change her sweet roles packaging into more diverse one. That was the time she then appeared on a movie as a sexual predator entitled Casualty of Love, The Amy Fisher Story. She gained more mainstream success in TV as Jennifer Mancini on Melrose Place, Meg Winston in Spin City and most notably as Phoebe Halliwell on Charmed. Both she and Holly Marie Combs became producers for Charmed during the show's fifth season, with whom Alyssa has maintained a strong friendship. In 2007, Alyssa appeared in ten episodes on the show My Name is Earl. This reunited her with Jaime Pressly who guest starred in the Season 5 premiere of Charmed, A Witch's Tail. Alyssa also began appearing on television again in commercials for Veet and SheerCover. She was cast in a new comedic television show, The Untitled Kristin Newman Project, for the 2008-2009 season.

Outside of acting, her hobbies include photography, humanitarian work and spending time with her three dogs and eight horses. Alyssa is an avid fan of the Los Angeles Dodgers. In 2007 she created her own signature "Touch" line of team apparel for female baseball fans, currently available on Major League Baseball's website, along with her own baseball blog. She was recently appointed Founding Ambassador for the Global Network for Neglected Tropical Diseases to which she donated $250,000 of her own money, and she is also also a UNICEF Goodwill Ambassador for the United States. She traveled to India, as well as Angola, to work with UNICEF field officers there. Alyssa is also a strong vegetarian and appears in numerous PETA advertising campaigns for vegetarianism!

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Trivia

- Alyssa  was given two nicknames: Lyssie and Conan.
- She went to the Bel Air Preparatory School and The Buckley School in Sherman Oaks, both located in California.
- In 1988 she had a best-selling exercise video called Teen Steam.
- Her favorite TV show is "ER", and her favorite movie is "It's a wonderful life".
- She supports the New York Knicks and L.A. Lakers.
- In 1989, a picture of her was used to create 'Ariel' in the classic Disney movie "The Little Mermaid".
- She is also a singer and recording artist, though not in her home country (USA). She has released five albums that have all reached sales of over 1 million copies in Japan.
- Her favorite saying is: "It's nice to be important, but it's important to always be nice".
- She suffers from dyslexia and is allergic to soy products.
- Her ex-husband, Cinjun Tate, is the lead singer for the rock group, Remy Zero.
- Holly Marie Combs and Shannen Doherty were her bridesmaids at her wedding to Cinjun August Tate.
- She plays piano and flute.
- In 2005, she was ranked #5 in E's 50 cutest child stars all grown-up.
- Her favorite sports are hockey and basketball.
- She is a friend of baseball pitcher Carl Pavano, who pitched for the Montreal Expos, the Florida Marlins and the New York Yankees.
- Alyssa is an active member of UNICEF.
- Her favorite bands are The Beatles, Dave Matthews Band, Del Amitri, and Remy Zero.
- She has a phobia of water, which made her underwater scenes in the episode of Charmed "A Witch's Tail" very hard.
- Out of what she called necessity, Alyssa teamed with G-III and MLB to create her own signature touch line of team-logo fashion for the female fan, which was released for sale on-line on April 13, 2007.
- She enjoys gardening topless because she loves being at one with nature.
- Her favorite book is  "Animal Farm" by George Owell.
- She has seven tatoos and a nose piercing.
- In February 2008, she wore a lettuce outfit for PETA's "Let Vegetarianism Grow on You" campaign in support of vegetarianism. She's a vegetarian!

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