'Normal' is meaningless. It just means 'in-range'. Just 'in-range' isn't the same as 'optimal'. But, if you aren't hypo, why did you post on a thyroid forum? Not saying that you shouldn't, but given that no-one else has answered, I think you can take it that no-one knows the answer to your question. We only tend to know about things to do with the thyroid. However, as I said, the dark circles can be a symptom of hypothyroidism. But, if it's not that, I doubt we can help you. Sorry.
Someone or may be something you have read I suspect may have lead to you joining this forum. And another remark suggests you may have had a retest already. These aren't akways easy to understand so if you have had a test in the past if will help if you can post it, and the ranges often in brackets after and we can probably help you more. Thyroid issues appear to be on the rise and it's easier to address them before much damage has happened to your thyroid. Its often more common in women but we do have male members as well.
When my son got allergy testing done the nurse told me that sometimes dark circles under the eyes indicates an allergy to something. In his case he wasn’t allergic to anything environmental but after doing a food intolerance test through our naturopath i found out he was dairy and gluten intolerant amongst a few other foods. Once we took gluten and dairy out of his diet the dark circles improved and his stuffed up nose and eczema cleared up as well.
Same for me, once I removed gluten, mushrooms, dairy and coffee my dark circles went. Coffee was also the culprit for my husband. I was able to reintroduce all but gluten as long as I didn't have them daily. I found the foods I use to crave were the ones I was intolerant to.
I found that dairy products cause dark circles under my eyes. They have been referred to as allergic shiners or a milk allergy. This includes all dairy products: milk, cheese, ice cream etc
Weakened adrenal glands will cause dark circles (and can be caused by food allergies and sensitivities as well as stress including work hours).
You should start taking care of your adrenals too. Look up adrenal cocktail. Also, there are supplements (vitamins and herbals) that feed the adrenals. They usually need lots of B5 and Vit c as well as some B6.
Hi there are many reasons for dark circles around eyes from tiredness, stress to anemia etc. When I was 25 I used to need to get at least 10 hrs sleep a night. If worried get blood test. Good luck 👍
Actually this topic has been discussed in depth previously. If you put "Dark circles under eyes" in the search box (top right) you will find lots of very in depth hypotheses.
My Endocrinologist mentioned weight loss would make shadows around my eyes more noticeable. Sensitivity to skin products I was using for dry skin on my face seemed more likely to me. If you are using any commercial products on your face try another brand with simple ingredients.
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Dark sunken eyes hypothyroid
Still going around in circles, very confused
Under Eye Bags and circles
Overactive thyroid symptoms! 
Sick of going around in circles 
