Firstly it would help if we knew which
shell you're using :)
I'll assume it's bash....
Here's an excerpt from "man bash" that
you should read carefully.
When bash is invoked as an interactive login shell, or as
a non-interactive shell with the --login option, it first
reads and executes commands from the file /etc/profile, if
that file exists. After reading that file, it looks for
~/.bash_profile, ~/.bash_login, and ~/.profile, in that
order, and reads and executes commands from the first one
that exists and is readable. The --noprofile option may
be used when the shell is started to inhibit this behav-
That means that if you don't invoke bash as a login-shell,
it won't touch .profile.
It also means that if it find's .bash_login, or .bash_profile,
it won't touch .profile either.