A picada de mosquito ainda me dá comichão.

In Portuguese, picada is the usual word for an insect bite or sting, including a mosquito bite.

• picada comes from picar = to prick, sting, bite
• mordida comes from morder = to bite with the mouth

So for mosquitoes, picada is the natural choice in Portuguese, even though in English we say bite.

A is the feminine singular definite article, meaning the.

It appears because picada is a feminine noun: a picada.

In this sentence, it refers to a specific bite, probably one already known from context, so the mosquito bite is a good way to think of it.

De mosquito is a general, classifying expression: mosquito bite.

It works like this:

• picada de mosquito = a mosquito bite / a bite from a mosquito
• picada do mosquito = the bite of the mosquito / the mosquito’s bite

So:

• de mosquito sounds more general and idiomatic
• do mosquito usually refers to a specific mosquito already identified in the conversation

Here, ainda means still.

So the idea is that the bite is still causing itchiness now.

In this sentence, ainda modifies the whole verbal idea: the bite still gives me itchiness.

Portuguese often expresses this idea with the structure dar comichão:

• dar = to give
• comichão = itchiness / an itchy sensation

So literally it is something like gives me itchiness, but naturally it means it still itches or it still makes me itch.

This is a very common Portuguese way of expressing physical sensations.

Because ainda triggers proclisis, which means the object pronoun goes before the verb.

So in standard European Portuguese:

• Ainda me dá comichão. ✅
• Ainda dá-me comichão. ❌

Without a word like ainda, dá-me would be normal in European Portuguese:

• A picada dá-me comichão.

This is an important word-order point in Portuguese clitic pronouns.

Me is the unstressed object pronoun used with the verb.

Here it means to me.

• dá-me comichão = gives me itchiness
• me dá comichão = same meaning, different placement because of ainda

Mim is used after prepositions, for example:

• para mim
• de mim

So mim dá comichão would be wrong.

Comichão means itchiness, an itch, or the feeling of wanting to scratch.

In this sentence it refers to the sensation caused by the bite.

A few useful notes:

• In Portugal, comichão is the normal word.
• Learners who know Brazilian Portuguese may have seen coceira, which is much more common in Brazil.

So comichão is a good European Portuguese word to learn here.

Yes, you can, but the meaning is slightly different.

• A picada de mosquito... = a mosquito bite / mosquito-bite type, more general
• A picada do mosquito... = the bite from the mosquito, more specific

If you are talking about one particular mosquito already mentioned, do mosquito can make sense. But as a general everyday expression, picada de mosquito is usually more idiomatic.

Because the present tense describes the current result or sensation.

The bite happened in the past, but the itch is happening now, so present tense is natural:

• ainda me dá comichão = it still itches / it is still causing itchiness

Portuguese often uses the simple present for ongoing states and sensations like this.

Yes, it sounds very natural in European Portuguese.

A few clues:

• comichão is especially typical in Portugal
• the clitic behavior in ainda me dá matches standard Portuguese grammar used in Portugal

A Brazilian speaker would understand it, but in Brazil you might more often hear different wording, such as expressions with coceira or coçar.