For those who are as intrigued as I am by the stretch marks on my Jalapeño chillies, I read the following on gardening.stackexchange.com.
“These “stretch marks” are the pepper equivalent of human stretch marks which form when the muscles & tissues expand at a different rate from the skin covering them (e.g., pregnancy marks or from excessive gym + protein supplements, etc). In this case, the flesh of the pepper fruit expands faster than the outer epidermal layer and the brown spots are from “healing” (the equivalent of our scabs). They are perfectly normal and there is nothing you need to do about it (or can do about it).
I’ve read from more than one source (and experienced it myself), that peppers with stretch marks tend to be hotter than those without (i.e., smooth skinned ones). This site also says the same:
Ever take home a jalapeño chile pepper from the grocery store and have it either be so lacking in heat it may just as well be a bell pepper, or so hot a speck will create a raging inferno in your mouth? Here’s a quick tip for choosing jalapeños that can help you decide which ones to pick. Jalapeño chilies start out mild and progressively get hotter the older they get, eventually turning bright red (and quite hot). As they age, they develop white lines and flecks, like stretch marks running in the direction of the length of the pepper. The smoother the pepper, the younger, and milder it is. The more white lines, the older and hotter. Red jalapeños are the most hot, because they’ve been maturing the longest.”
I love it! It explains why my Jalapeños are so hot when I expected them to be mild. I pickled 3 jars of green ones today so maybe they will be mild. I also pickled another couple of jars of red ones … oh, well …. they can be for the days I want a bit of fire.
Passion Fruit Garden 
I have always wondered why jalepenos range in heat very hot to no heat at all. Out of all the different reasons and conditions
the most logical to me is that the plants produce more heat when “stressed” by low moisture. My theory as to why is simply that in drought like conditions the plant turns up the heat to ward off insects/animals who may not usually consume it, but are driven by desperation in drought. Citrus growers report sweeter fruit in drought like conditions which supports my theory. Why? Because citrus bearing trees attract consumption to spread their seeds. Citrus seeds are dense and pass through an animals system, jalepenos and other like peppers are delicate and would be destroyed.
Hi Merit. My Jalepenos are growing in my vegie patch and during the summer they were watered everyday. There was no drought in my vegie patch and my Jalepeonos were extremely hot.
Again, only a theory. But the optimal word in drought like conditions would be “like” . Most of us don’t rely on rainwater and can control moisture application and retention. In some climates watering everyday is not but a sip to plants. Another thing to consider is the number of different strain variations within the jalepeno family. If you are able to get hot peppers (and thats how you prefer them) consistently with your regime, then good for you.
Hi Merit. Actually, I was looking for mild ones:(
Well, I never! Chillies with stretch marks .. You’re full of surprises, Glenda.
Hi Christine. It seems stretch marks on jalapenos are common.
thanks for sharing that Glenda, fascinating indeed!
Hi Lisa. It is interesting.
I’d no idea. Thanks, Glenda.
Hi John. It is interesting.
thanks Glenda, I was losing sleep over that one. Seriously I have grown chillies and found stretch marks, I ignored them until now. But at least it is nothing to worry about.
Hi Roz, It is so interesting how they get hotter as they age. I wonder if it is the same with other chillies.
Well, what do you know! Very interesting – I’ve always thought that the reason why our local jalapenos are lacking in heat was because of our climate – and in a way, it is – but now I know that if our climate was hotter, the jalapenos would grow faster and therefore get picked later, and be hotter. Live and learn.
Hi Doc, That is also why the bottled ones are mild. They are pickled green.
I’m glad you found the answer Glenda!
Hi Anne, It is interesting so I thought I would share.