Your dry lips could be a result of an allergic reaction. Lipsticks that contain ‘propyl gallate’ could be the culprit, this substance is an anti-oxidant that is commonly used in cosmetics and many people are actually allergic to it. If this comes up on the ingredients in your favourite lipstick then try one that doesn’t contain it and see if there are any improvements to your lip health. If there is then I’m sorry to say you will have to get rid of any product containing propyl gallate as you are probably allergic to it.
Toothpaste is another source of possible allergy. If the product you use contains guaiazulene or sodium lauryl sulfate this may be the source of your problems. Guaiazulene is used as a blue dye in toothpaste and is also useful as it has anti-viral and anti-oxidant properties. However, if this chemical has long term contact with the skin it can cause irritation and in some individuals it can cause a sever reaction that can lead to cheilitis. If this happens then a trip to your local medical practitioner is highly recommended. Sodium lauryl sulfate is a cheap foaming agent detergent that is used in a lot of personal hygiene products, including toothpaste. This is good for cleaning the teeth but bad for sensitive lips. Sodium lauryl sulfate is an irritant because it is a detergent, if you have generally sensitive skin then you are at extra risk of getting dry lips from using toothpastes with this chemical in.
Some foods can also hinder your lip health. Figs are common in causing allergic reactions that can look like chapped lips, also some metal can induce a reaction. Try not to put metal pens or paperclips in your mouth. Also acidic foods such as lemons and oranges could irritate your lips and cause them to dry out. Ultimately discovering what allergies causing dry lips for you is the biggest problem you may have and will have to overcome in your lip care regime.