http://www.doctoroz.com/blog/audrey-kunin-md/many-hidden-causes-chapped-lips



Check for periodontal disease or abscesses. There are reports that deep cleansing of the mouth performed by the dentist (possibly under anesthesia) may help solve the problem.
Clarinet players may develop chapping at the contact area of the reed.
The ingredient propyl gallate in lipstick may be causing a contact allergy.
Your toothpaste may be to blame if it contains guaiazulene
Check out the ingredient label on your toothpaste. If it contains sodium lauryl sulfate, this may be a concern as well. Blamed for chapped lips, skin irritation and even perioral dermatitis, avoidance of sodium lauryl sulfate can be helpful.
A little known (or seen) condition known as chelitis granulomatosa may require a biopsy for diagnosis.
Being allergic to nickel may surface on the lips too. Remember; don't put metallic items like paper clips in your mouth!
The juice from citrus fruits may cause both irritation as well as a sun sensitive allergy that looks like chapped lips.
Eating figs can result in a light allergy.
An ingredient known as phenyl salicylate (salol) used in lip care products may be your culprit.
You can develop an allergy to cobalt from taking vitamin B12 supplements. It may look like unexplained episodes of recurrent swelling and crusting of lips made worse by wind and sun exposure. And it is important to know that you may have a negative patch test to vitamin B12 despite the presence of the allergy.
The blood pressure medication propranolol may cause chapping as a side effect.
If you've got vertigo and chapped lips, check to see if you're on the medication prochlorperazine.
Down's syndrome patients have a genetic predilection to having chapped lips. Treatment with thyroid supplement and potent topical steroid ointments may clear the condition.
All those years in the sun may have caused precancerous changes known medically as actinic chelitis. Treatment with a topical chemotherapy medication known as 5-flourouracil may clear it up.
An allergy to red dyes used in candy, mouthwash, toothpaste, etc. may be to blame.
On the same note, cinnamates (the source of cinnamon flavor) used in candy, lozenges, gum, mouthwash and toothpaste may be to blame.
Do you snore? Enlarged tonsils, adenoids or sleep apnea may be to blame for those lips. That continuous flow of breath across your lips all night long can grossly dehydrate your lips. If you don't know if you snore, it may be worthwhile to have someone check on you periodically during the night to find out. Consider applying a protective barrier on your lips come bedtime.
Do you have Psoriasis or lichen planus? Believe it or not, unusual cases of either may involve the lips. If the scale and crusting is particularly thickened, this could be the culprit.
Is there scaling and cracking at the angles of your mouth? This is known as perleche and is due to a yeast infection which could involve the rest of the lips as well. Treatment with a prescription oral anti-yeast preparation should do the trick. Diabetics are particularly prone to this condition which may be recurrent.
Do you have lupus or a history of autoimmune disease? Photosensitivity may present itself on your lips. Wear a lip balm that includes a minimum SPF 15.
Are your eyes dry and your mouth dry? You may have an autoimmune condition known as Sjogren's syndrome.
Have a history of thyroid disease? Hypothyroidism can cause dry skin and lips.

Too much vitamin A whether in oral supplements, prescription medications like Accutane or too much in your diet may lead to peeling lips. Check the label on your supplement. If you're taking more than 25,000 IU a day, you may have found your cause.

Do you take out your stress by habitually licking or chewing your lips? Continuous contact with saliva can lead to both dehydration as well as irritation due to the enzymes present that are meant to aid in digestion. Many people are totally unaware of this habit. Sometimes this even happens during sleep. Be candid with family and friends if you're uncertain and ask them. Find out how good a friend they are, and have someone check you periodically when you sleep too. Sometimes antidepressants or relaxing medications may be required. Often times, simple awareness of the situation goes a long way to kicking the habit.


Don't You Dare

Still haven't gotten to the bottom of the cause? While you wait for your dermatology appointment for further workup, follow the don't list:
Don't hold metal objects in your mouth such as paper clips.
Don't lick envelopes.
Don't suck on citrus fruit rinds such as orange peels.
Don't kiss someone on the lips who is wearing lipstick.
And finally, don't lose hope!