The Dark Shadows actress, who will celebrate her 19th anniversary with husband David E Kelley this year, admitted that she does not trust easily and tries to protect herself from the "intense scrutiny" of the public.
"It takes years for me to trust; I know that about myself. A lot of it is because I am so private, and so reluctant to make myself vulnerable. You have to be vulnerable to have real intimacy with people. It's a two-way street, you know? Eventually I do get there, but not with very many people. I have it with David, of course," Pfeiffer explained to Parade.
"It is part of the hand you're dealt when you become a celebrity. Nobody would consciously decide to become guarded and self-protective. I was very open when I was younger, but celebrity teaches you. You learn to cope with the intense scrutiny."
Asked if it is possible to be entirely sure of a partner's loyalty, Pfeiffer added: "Sometimes you know and sometimes you don't. All humans are subject to denial. Everybody is vulnerable to being in relationships where they get fooled. I'm no different. It's just human nature."
Pfeiffer recently received the 2012 Cinema Icon Award at the CinemaCon convention in Las Vegas.
Watch the trailer for Dark Shadows below: