Summarize:

Sneezing is one of your body's natural defenses to get rid of foreign invaders. The same physical reaction occurs for both allergens and cold viruses, so sneezing is generally not the best way to determine whether you have allergies or colds. However, if you are sneezing and have some of the other symptoms listed in either the cold or allergy sections of this article, you can make a better guess at what you are dealing with.  When foreign invaders (like pollen or a virus) get trapped in the tiny hairs of your nose known as cilia, the invaders can begin to tickle your nose. This tickling sensation can make your brain trigger a sneeze to get rid of the invaders. By sneezing, the allergens or virus are expelled from your nose. Some of the most common allergens that cause sneezing include: dust, pollen, dander from the fur of animals, and mold. While this might sound gross, it really can help you determine whether you’re dealing with a cold or allergies. When you get infected with a virus, or get bad allergies, your nose will get stuffed up and start running. When this happens, take a look at the color:  If it is clear, it is likely that you are dealing with allergies. Yellow, green or greyish mucus generally comes along with a cold. Sinus pain refers to an aching or sharp pain or pressure that you feel in your nose, eyes, and forehead. Your sinuses are hollow air spaces in your forehead, behind your cheekbones, and between your eyes. The sinuses release mucus that attempts to keep allergens and other foreign bodies out.  If your body’s immune system releases histamine, your sinuses may become inflamed, leading to this sinus pain. Your sinuses can also become painful because of a cold. This is because your the virus causing the cold can infect your sinuses. Your tonsils are essentially two masses of tissue that filter and trap germs and other microorganisms (like allergens) as they enter your airways. These tissue masses are found in the back of your throat and can also produce antibodies to fight infections. If a large amount of microorganisms, such as a virus causing a cold, get trapped in your tonsils, your throat can become infected.  If you are dealing with a cold-caused sore throat, your throat will most likely feel raw or tender. You may have a hard time swallowing. If you have an itchy throat caused by allergies, your throat will most likely feel like you need to scratch it like you would an itch on your skin. When you are dealing with a virus or allergens, one of your body’s natural reactions is to develop a cough. This is especially true if the infection or allergen has reached your respiratory system.  A cough caused by a cold might become productive, meaning that you begin coughing up phlegm. A cough caused by allergies is generally dry, meaning that you don’t cough up phlegm.
Note that sneezing occurs both when you have allergies and when you have a cold. Look at your mucus when you blow your nose. Monitor any sinus pain you feel. Consider whether you have a sore throat or an itchy throat. Pay attention if you are coughing a lot.