[Gogetit (OP)]

especially when you're sick with common cold, you get runny nose whenever sneezed. why do nose run when we sneeze?

[Chemistry4me]

Your nose is sort of like a big washing machine. When something irritates the inside of it, it tries to wash it away. A few things that can cause your runny nose are a cold, allergies, or an infection. Sneezing is also a way of removing things that your body doesn't want.

[Gogetit (OP)]

but why do sneeze and runny nose go together? like particles come out from your nose right when you sneeze. why is that?

[Chemistry4me]

I'm not quite sure what you mean. When you sneeze, there is a huge rush of air outwards and it drags the particles out with it.

[Chemistry4me]

Get back to me if I haven't explained it very well.

[Gogetit (OP)]

so that huge rush of air come out from not only your mouth but also your nose?

[Chemistry4me]

Exactly

[Richlv]

It seems to me that this has not been sufficiently explained. Some 10-20 seconds after sneezing the nose starts running quite heavily. The intensity of this is the surprising part.
I don't recall having that many years ago, but maybe running nose was not something to pay attention to during childhood - or maybe it is a sign of some health issue regarding the nose

[chris]

There are several reasons why this may happen. The most likely is that the same stimulus that provoked the sneeze also provoked the runny nose, albeit more slowly in the latter case.

Specifically, the lining of the nose is richly endowed with mast cells; these are charged with histamine. When anything irritates or perturbs the mucosa (lining) - and this can be a viral or bacterial infection, inhaled dust or allergens, foreign bodies or parasites, these cells discharge their histamine cargo.

Histamine has several actions. One is to profoundly irritate the sensory nerves that supply the nose lining; this irritation can trigger a sneeze. Histamine is also vaso-active; that is, it acts on blood vessels to make them dilate and become leaky. This has the effect of increasing blood delivery to secretory glands in the mucosa. Histamine also directly triggers mucus production by these same glands. These latter actions take longer to initiate than a sneeze reflex; hence you sneeze first, then blow your nose later...

[Richlv]

Thank you for the response. My initial reaction was "I instinctively feel this cannot be right" , but thinking more properly about it, sometimes a sneeze that fizzles still ends in a running nose. Thank you for the answer.