All of the symptoms of iodine deficiency are related to its effect on your thyroid. Your thyroid is a gland in your throat that regulates your metabolic processes, such as growth and energy in your body. If you don't have enough iodine in your diet, this can lead to iodine deficiency disorders such as: Goiter: This is when your thyroid enlarges, or develops a goiter, as it tries to keep up with the demand for thyroid hormone production in your body. Iodine deficiency is the most common cause of goiter. If you have goiter, you may experience symptoms like choking, especially when lying down, and difficulty swallowing and breathing. Hypothyroidism: This is when you have an underactive thyroid gland, as your thyroid can't make enough thyroid hormone to keep your body running normally. If you have hypothyroidism, your body's processes will start to slow down. You may feel colder, tire more easily, your skin may get drier, and you may become forgetful or depressed. The symptoms for hypothyroidism are variable so the only way to confirm you have this disorder is to get a blood test. Patients with thyroid disorders should not automatically start an iodine supplement because there are certain types of thyroid disease that are contraindications for iodine supplements. Pregnancy related issues: Severe iodine deficiency (which is extremely rare and even unheard of in the United States) in mothers has been associated with miscarriages, stillbirth, preterm delivery, and congenital abnormalities. The children of mothers with severe iodine deficiency during pregnancy can have mental issues and problems with growth, hearing, and speech. In fact, even mild iodine deficiency during pregnancy may be associated with low intelligence in children. Iodine is released from your body when you pee. Thus, the best way to determine if you have iodine deficiency is to speak to your doctor and have her do tests on your urine. She will then be able to look at the results and check if you have an iodine deficiency based on the iodine concentration in your urine sample. If you already have thyroid problems, like hyperthyroidism, too much iodine can actually worsen your thyroid disorder. Follow the minimum amount of iodine required for you, based on your age and gender. Adults should not exceed 600 mcg/day of iodine to avoid consuming too much iodine. Some people who move from an iodine-deficient region, such as parts of Europe, to a region with higher levels of iodine, such as the United States, may also develop thyroid problems since their thyroids have gotten used to taking in small amounts of iodine. This may then put them at risk of developing hyperthyroidism.
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One-sentence summary -- Recognize the symptoms of an iodine deficiency. Get tested for an iodine deficiency. Be aware of the health issues associated with consuming too much iodine.

Bringing your question up on a whim might not give you enough time to talk. Invite your parents to have a formal conversation. Your parents will see how serious this is for you, as well as how much you value their decision. If they say now isn't an ideal time, set up a scheduled conversation with them later on. You could say, for example, "Hey, Mom and Dad. I have a question for both of you. If you're not busy, can we talk tonight at around seven?" Look through your notes and pick one of your strongest talking points. Tell them how much you loved your first piercing and how you've thought about getting a second. Let them know how much your respect their authority, and ask them what their opinion is. A sample conversation could look like: "Mom and Dad, remember how I got my ears pierced last December? Well, I want to get my upper ear pierced, too. I think upper ear piercings look really stylish and are low-maintenance to take care of. The last thing I want to do is get pierced without your permission. What do you think?" Your parents, especially if they dislike piercings, might have a perspective opposite of your own. Don't launch into a yelling match. Instead, listen to them. Let them know what points of theirs you agree with, and show them that you understand their point. Bring up your own points in response with a level and empathetic head. If they say tongue piercings get infected easily, for example, you could say, "Thanks for thinking of my safety. I know that tongue piercings are harder to take care of, but I've taken care of my earrings for two years with no infection. Plus, I looked up proper tongue ring care for the first six months." Even after explaining your points, your parents still might feel wary about multiple piercings. Maybe they feel like piercings are expensive, or maybe they don't agree with where you want a piercing. Try to meet them in the middle and find a resolution that works for both sides. If they're worried about the money, for example, offer to do chores around the house or babysit for the neighbors. Remember to keep your end of the bargain. If you forget, your parents may judge you as irresponsible. Even if you don't agree with your parents' decision, don't raise your voice or insult them. In most cases, your parents have your best interest in mind. If the conversation gets to heated, ask your parents if you can resume talking about it at another time. When you and your parents are upset, neither side is going to listen. Actions are just as important as words. Avoid rolling your eyes, scowling, or shaking your head at your parents.
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One-sentence summary --
Ask your parents to talk, when the time is right. Explain to your parents what you want and why. Validate their argument. Make a compromise, if your parents are hesitant. Stay calm and respectful.