Can anybody telling me why in the whole English language only 'Asthma' has four constants without any vowels in between/

Even foreign names entering the language must have vowels between any two or three letters.

eighth (4), offspring (5), hamstring (4).

And have a look at "hymn". It has a vowel sound, that's true; but there are no vowels in the spelling.
'Strength' is also in the English language. 'latchstring' has 6 consonants together, although it is really two words conjoined.

'Asthma' was the original greek spelling I think, so that's probably why it has stayed that way. I'm not aware of any barriers against letter combinations entering the language, other than ease of use.
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