TIn the last few days, I've been taking morebetter care of my skin, mostly ion my face.

This sounds more natural

So, I've been applying some serums for acne, exfoliation, and opening pores.

I had read on the instructions that I must be sovery careful when I applying them, avoiding the face's sensitive parts.

I thought it was a myth, but I’ve already found out that it's not - in the most horrible way.

One night, I applied one of these serums without being more careful, I didn't notice that I also applied a bit of it on my lips edges, and like this I went to sleep like this.

Just some sentence structure errors

I woke up with my mouth souper sensitive, with a chemical burn inaround all the edges.

“In all the edges” sounds odd

Today, what hurts me are the corners of my lips hurt, and because it's a wet area, withich movemens a lot, it's so difficult to cursoothe.

1. Saying something like “My ___ hurt(s)” is the most common way to say something hurts in English
2. The rest is hard to explain, but I changed it to sound more natural

I must be sovery careful with the skincare steps because I read that's so easy to get infected and to have fungus.

So, in summary, the next time I'll follow the usage instructions exactly to the letter of the products.

I’m not sure “to the letter of” means. Is it an English phrase or a Spanish phrase you directly translated?

If there's a warning, it's for a reason, and I don't want to to confirmfind out if thesey are true or not.

“To find out” sounds better than “to confirm” in this context

The last few days, I've been taking morebetter care of my skin, mostly ion my face.

As an ordinaryLike most womaen, I have acne about once a month.

Just switched it to a bit of a more natural phrase. You'd also want to say "about once a month" unless you're being precise and you only get acne one time a month each month.

I had read on the instructions that I must be so careful when I apply them,to avoiding the face's sensitive parts. when I apply them

Just a little switch in the order of the words here, again to sound more natural.

One night, I applied one of these serums without being more careful,. I didn't notice that I also applied a bit of it on my lips edges, and like this I went to sleep like this.

I made these into two separate sentences. Also, just changed the order of the words in the second sentence to sound more natural.

When I woke up with, my mouth waso sensitive, withand I had a chemical burn in all the edges.

Not a necessary correction, just flows a bit more easily.

Today, what hurts me are the corners of my lips hurt, and because it's a wet area, with movemen that moves a lot, it's so difficult to cure.

I must be so careful with the skincare steps because I read that's so easy to get infected and to haveget fungus.

If there's a warning, it's for a reason, and I don't want to to confirm if these are reason is true or not.

TFor the lpast few days, I've been taking more care of my skin, mostand concentrating especially ion my face.

As an ordinary woman, I haveget acne once a month.

For diseases, "get" is more commonly used than "have".

So, I've been applying some serums for acne, that exfoliation,e my skin and open my pores.

Since it's the acne serum that's presumed to also do the exfoliation and the pore opening, this is how you phrase it.

I had read on the instructions that I must be soreally careful when I apply them, serum, by avoiding the face's sensitive parts.

I thought that it was a myth, but I alreadyhave just found out that it's not - —in the most horrible way.

One night, I applied one of these serums without being more careful,. I dihadn't noticed that I had also applied a bit of it on my lips edges, and like thisthe edges of my lips, and then I went to sleep just like that.

I woke up with my mouth sofeeling sensitive, with a chemical burn ion all the edges.

Today, what hurts me are this day, the corners of my lips, and b still hurt. Because it's a wemoist area, with movement, it's so difficult to cure still hasn't healed properly.

Now, I boughthave to buy other products for my poor, burned and irritated lips.

I must be sohave be careful with themy skincare stepsregimen, because I have read that's so it's easy to get infected and to havewith fungusi.

So, iIn summary, the next time, I'll follow the usage instructions exactly to the letter of the productsas written.

If there's a warning, it's there for a reason, and I don't want to to confirm if these areit's true or not.