Why do you see bright flashes of red during IPL treatment of the face even with complete blackout eye protection?

I had IPL treatment on my face with black out eye goggles covering my eyes and my eyes closed underneath. I found it odd that with each flash I could still see VERY bright red light. That was alarming. How does this light reach your eyes with all that protection? Is it harmful? My hypothesis is that it is reflected light that actually migrates through and under the skin to reach the eyes behind the covers. I can't think of any other explanation because the covers were very tight with no gaps.