Pragma

The Pragma header is the primary method for controlling caching behavior in HTTP/1.0. Because HTTP/1.1 introduces the more flexible Cache-Control general header, use of the Pragma header is dwindling. Most developers who make use of the Pragma header do so as a safety measure only in order to support Web clients that might not be compliant with HTTP/1.1.

Additionally, because the Pragma header was replaced as more control over caching became necessary, it was only implemented with one possible form:

Pragma: no-cache 

Although other forms are allowed by the specification (in order to remain flexible to future implementations), the use of the Cache-Control general header has curtailed the use of any other forms of the Pragma header.

When used in the way just illustrated, all intermediate proxies are to forward the HTTP request to the origin server rather than replying to the Web client with a cached copy.

According to the HTTP specification, this header is intended to be used in HTTP requests as a way for the Web client to indicate that it wants the request forwarded all the way to the origin server. In practice, however, it is also used by Web servers to indicate that the HTTP response should not be saved in a caching system, and support for this behavior is fairly consistent.