Thyroid issues do not cause ridges on the nails, but these issues might cause the nails to become brittle or split from the nail bed, according to MedlinePlus. Conditions such as anemia, injury and arsenic poisoning may cause ridges on the nail.
Most nail issues are not dangerous, but a person must see a doctor in some cases, such as if the ridges on the nail are horizontal, explains MedlinePlus. Other issues that may be a sign of a dangerous condition include nails that have a dark streak in them, nails that are abnormally pale, or nails that have pits or are turning blue.
When seeing a doctor, a person must expect to answer a number of questions such as how long the condition has gone on or if there are changes in the thickness of the nail, states MedlinePlus. A doctor may also ask questions about recent injuries, if a person bites or chews on the nails, or if the nails often have nail polish on them. Tests to determine the cause of damaged nails include X-rays, laboratory tests, blood tests and visual examinations. It is possible to prevent many nail issues by avoiding biting the nails, keeping the nails short and strengthening the nails with a biotin or other protein treatment.