A damaged skin barrier causes skin irritation and results in skin conditions such as excessive oiliness, a tight feeling, inflammation, redness/irritation, sensitivity, or even acne. It’s an open invitation for external irritants and bacteria to get into the skin, weaken it and disrupt it from functioning properly. Your skin loses essential nutrients (such as water) at an alarming rate — this is also called transepidermal water loss (TEWL).
On the other hand, a healthy skin barrier is resilient and protects us from harsh elements such as daily environmental assault (UV rays, pollution, bacteria, toxins), poor lifestyle choices (diet, stress, lack of sleep). But more importantly a healthy barrier retains water/moisture in the skin making it look and feel radiant and glowing.
First off dry skin is a skin type, whereas dehydrated skin is a condition.
Dry skin is genetic and stays the same irrespective of the season (during winter months it gets drier). Dehydrated skin is a temporary condition and can be easily treated with the right products.
Dry skin needs thicker creams, balms, and facial oils to make up for the lack of natural oils/sebum. If you use a hydrating serum only (e.g., Hyaluronic acid) your dry skin will get worse.
Dehydrated skin on the other hand needs hydrating products i.e., water-based serums (e.g., Glycerin, Hyaluronic acid) and toners to make up for the lack of water in the skin. And don’t forget to drink lots of water to hydrate from the inside.