Hypothyroidism is notoriously difficult to detect and manage, especially in its earliest stages. It's entirely possible to have "normal" levels of thyroid stimulating hormone, also known as TSH, but have signs and symptoms of hypothyroidism . It's also possible to have "high" levels of TSH without any or many of the usual symptoms of hypothyroidism , such as weight gain, feeling cold all the time, dry skin, and chapped lips.
If you are elderly, sometimes the first sign you have thyroid disease is a cardiovascular problem. In fact, the symptom that is easiest to prove to be linked to low thyroid hormone levels is heart disease .And at any age, it's not unusual for thyroid stimulating hormone measurements to be just plain wrong. "Normal" readings are found in standard lab tests for about 20 percent of people would be prescribed thyroid hormone replacement if they received the most modern TSH testing . When it comes to getting a diagnosis of hypothyroidism, sometimes you should not be in a hurry to take the doctor's "no" for an answer.
Thyroid hormone replacement will probably get a quick relief
If you have hypothyroidism, simply getting thyroid hormone replacement, usually Synthroid, you will probably get quick relief from a long list of usually vague symptoms in addition to chapped lips:
- Blurred vision
- Cold intolerance
- Decreased appetite
- Decreased hearing
- Decreased perspiration
- Dry skin
- Emotional lability, mental impairment
- Fatigue, loss of energy, lethargy
- Forgetfulness, impaired memory, inability to concentrate
- “Lump” in the throat, hoarseness
- Hair loss
- (In women) menstrual disturbances, impaired fertility
- Joint pain, muscle pain, weakness in the extremities
- Prickly or tingly sensations in the hands and feet (paresthesia) and nerve entrapment syndromes
- Weight gain 
Sometimes, however, just treating hypothyroidism is not enough
O’Brien’s granuloma is a condition causing chapping and chafing of the lips and breakdown of the skin on rings on the face and neck . It is linked to hypothyroidism, but it is triggered by sun exposure . If you don't use sun protection, you can't heal your chapped lips and protein-deprived skin.
Iodine deficiency can cause chapped lips, dry skin, weak reflexes, swelling around the eyes, and, if it goes on long enough, loss of mental functions. It's not hard for people in many countries to avoid iodine deficiency. Simply use iodized salt. It may not remove goiter (enlargement of the thyroid gland), but it usually improves mental health in just a few months .To be sure, some health experts claim that iodized salt is not enough for good health, but it's a very good place to start when simple chapped lips remedies and other commonsense interventions just don't work.
Plummer-Vinson or Paterson-Kelly syndrome is an iron deficiency syndrome that can strike women after the age of 40. It causes an odd variety of symptoms including lip irritation at the corners of the mouth, "webbing" of the esophagus that makes swallowing difficult, weakness, pallor, and a rapid heartbeat. Usually iron supplementation is enough to reverse the disease, but sometimes it is necessary to rupture the "webs" on the esophagus. Iron supplementation will correct lip irritation and other cosmetic issues. 
Johanson-Blizzard syndrome is a devastating condition that has to be inherited from both parents. It causes irritation of the lips, but far more troubling are the beak-like nose, small cylindrical teeth, failure of skin on the scalp to grow, failure of the pancreas to release digestive enzymes, and hypothyroidism. This syndrome is not impossible to treat, but it requires intensive medical care beginning at birth. 
Chapped lips can also be a complication of treatment for thyroid cancer. Usually thyroid cancer is among the most treatable of all cancers, but when it becomes "anaplastic," a kind of rapidly growing blob of cells that aren't easily recognizable as coming from the thyroid, it can be deadly in a short time. Ordinarily thyroid cancer can be treated relatively simply with radioactive iodine, but in some cases the cancerous cells "forget" that they are part of the thyroid. To help cells "remember" their origins, doctors use a treatment called retinoic acid. 
Retinoic acid is basically a very potent form of vitamin A. It's very close to the compounds used to treat cystic acne. Any particularly potent form of vitamin A, however, will cause drying and chapping of the lips and skin. These treatments will usually cause redness, itching, and inflammation. They are decidedly preferable to cancer, however, and it's possible to deal with the effects on lips with generous application of chapstick, avoiding brands with strong flavors or lip balm ingredients you should avoid.