The hair at your hairline is the most fragile hair on your head. It's the finest, it has the least density, and it sits exactly where your protective styles exert the most tension. Losing edge hair is one of the most common consequences of protective styling done incorrectly, and it's one of the hardest things to grow back once it's gone.
Here's what you can control.
Before the Install
The most important thing you can do before any protective style is start with healthy edges. Edges that are already thinning or tender before an install will not survive the tension of braids. Give them time to recover with scalp oils, gentle edge massages, and low-manipulation styling before booking your next appointment.
If you're going to a stylist, tell them your edges are sensitive before they start. Show them where you're seeing thinning. A good stylist will adjust their technique accordingly. If they don't, that's information.
During the Install: What to Watch For
Braids that pull at the hairline should hurt noticeably. Not the mild discomfort of tight braids right after installation: actual pain. If you feel your edges being pulled taut during braiding, speak up immediately. Once the braid is in, the damage is being done with every hour it stays at that tension.
Ask your stylist to leave the edges out or to braid them with less tension than the rest of the style. A common compromise is leaving a small "perimeter" of your natural hair unbuttressed and unbraided at the hairline, which protects those fine hairs entirely.
During the Wear: Daily Care
Your edges are still your natural hair underneath the braid. They still need moisture. Apply a lightweight edge oil or a water-based leave-in along your hairline daily. Jamaican castor oil and rosemary oil both have some evidence for supporting hair growth and scalp health and can be applied directly to the edges.
Do not slick your edges down tightly with edge control products and then wear a tight scarf or headband to sleep. The friction and tension together on fine hairline hair is a recipe for breakage. Wear your satin bonnet over loose edges, not compressing them.
At Takedown
Be patient removing braids, especially around the edges. Cut the knot at the bottom if necessary rather than unraveling aggressively. After the braids are out, detangle the edges gently with your fingers before any tools. The hair that was protected inside the braid is fragile when first released: treat it like baby hair, because in some ways it is.
If Your Edges Are Already Thinning
Stop any style that puts tension on the hairline. Give the area a minimum of 60 to 90 days without braids, weaves, or tight updos. Massage the scalp at the hairline daily with a combination of castor oil and rosemary oil. Both have shown supportive effects on hair follicle activity in studies. If thinning doesn't improve after three to four months of this, see a dermatologist. This is a medical question at that point, not a product question.