Weird patterns developing on the sidewalls of my tyres

The tyres are 4 years old and may have run about 20,000 km.

BHPian androdev recently shared this with other enthusiasts.

Noticing this weird pattern on my Pirelli Centurato P7 235 55 R17 tires (S class). No other issue other than this visual patch, all around the circumference on all four tyres. The tyres are 4 years old and may have run about 20,000 km. It may have happened after a long highway drive, but I couldn't be sure. No bad roads involved. It doesn't look like any structural damage to me, but some oils coming out - any idea what this could be?

I am thinking of changing the tyres as a precaution and have the option of Michelin Primacy 4 ST. These would be imports from Thailand, I guess. How do they compare to Michelin tyres imported from Europe (with which I have had very good experience)? I used Michelin Energy (made in Thailand) on smaller cars and they didn't particularly stand out.

Here's what BHPian Chetan_Rao had to say on the matter:

You may want to look up 'tire blooming'.

Blooming is just one possibility. He did say it's happened to all 4 tyres which makes curb-rash unlikely, and he also didn't drive on bad roads before noticing this so it's a curious phenomenon.

Here's what BHPian Rahul Bhalgat had to say on the matter:

Tyre blooming is a discovery for me, I had never heard or come across this in all these years.

I found out that tyre blooming is the formation of brown deposits because of anti-ozonants in the rubber getting exposed to oxygen. But in none of the pictures about blooming, I could see the swirl marks like those in androdev's pics. The pics from the Google search showed uniform brown deposits on the blooming tyres. Is this blooming or some other chemicals coming to the surface?

As mentioned, the swirl marks are surprising. Did the sidewalls rub against some steps (like footpath)?

Here's what BHPian Emvi had to say on the matter:

From the images, the marks on the tyre appear to me as scuff marks. But on all four tires!? That's quite bizarre. I can only think of one reason, albeit a wild guess. Under-inflated tyres carrying decent to heavy loads may cause scuff marks on the sidewalls. Long ago, once it had happened so in my slow moving load carrier, I vaguely remember. I noticed such scuff marks on under-inflated rear tyres of my vehicle, after a few trips of load hauling back then.

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